Synchronization for satellite system

ABSTRACT

Synchronization technology is implemented for a satellite communication system. Master clock information is accessed at a terrestrial location. A timing message based on the master clock information is transmitted from the terrestrial location to a satellite as the satellite is in orbit. The satellite is synchronized to the master clock based on the timing message. A beacon signal is transmitted from the satellite toward Earth. The beacon signal includes timing information. The beacon signal is received at a ground based gateway. The gateway is synchronized to the satellite based on the beacon signal. Communication is sent from the gateway to a terminal via the satellite. The communication includes timing data. The terminal is synchronized to the gateway based on the timing data.

This application claims priority to U.S. Provisional Application No.62/314,938, “Non-Geostationary Satellite Constellation CommunicationSystem,” filed on Mar. 29, 2016, incorporated herein by reference.

BACKGROUND

The present disclosure relates to technology for satellite communicationsystems.

Satellite communication systems typically include one or more satellitesand a set of ground terminals. Such systems typically operate withinregulations that allocate operating frequency bandwidth for a particularcommunications service and specify, among other things, a maximum signalpower spectral density of communications signals radiated to the ground.A growing market exists for provision of high data rate communicationservices to individual consumers and small businesses which may beunderserved by or unable to afford conventional terrestrial services.Satellite communication systems have been proposed to provide such highdata rate communication services. However, designing a satellite systemto meet these needs is challenging.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram describing one embodiment of a portion of asatellite communications system.

FIG. 2 is a block diagram depicting a satellite and its antenna system.

FIG. 3 depicts a beam map for a Field of Regard.

FIG. 4 is a map of the world, showing a constellation ofnon-geostationary satellites,

FIG. 5 is a map of the world, showing the beam maps for elevennon-geostationary satellites.

FIG. 6 is a block diagram of one embodiment of a communications payloadfor a non-geostationary satellites.

FIG. 7 is a block diagram of one embodiment of a digital channelizer.

FIG. 8 depicts an example embodiment of an uplink frequency plan forbeams away from the Equator.

FIG. 9 depicts an example embodiment of a downlink frequency plan forbeams away from the Equator.

FIG. 10 is a beam map depicting one embodiment of an assignment ofcolors (frequency band+polarization) to spot beams.

FIG. 11 depicts an example uplink frequency plan for beams at theEquator.

FIG. 12 depicts an example downlink frequency plan for beams at theEquator.

FIG. 13 depicts a beam map.

FIG. 13A is a flow chart describing one embodiment of a process foroperating a constellation of satellites with different frequency plansand different hopping plans between beams at the Equator and beams awayfrom the Equator.

FIGS. 14A and 14B depict example beam polarization maps.

FIGS. 15A, 15B, 15C, 15D, 15E and 15F depict example beam maps.

FIG. 15G is a flow chart describing one embodiment of a process foroperating a satellite communications system, including changingfrequencies for subscriber terminals without the need to changepolarization as the satellites move with respect to the subscriberterminals.

FIG. 15H is a flow chart describing one embodiment of a process foroperating a satellite communications system, including implementingsatellite handovers.

FIGS. 16A, 16B, and 16C depict example beam maps.

FIGS. 17A, 17B, 17C, 17D, and 17E depict example beam maps.

FIG. 18 is a timing diagram describing time domain beam hopping.

FIG. 19 is a flow chart describing one embodiment of a process forperforming time domain beam hopping.

FIGS. 20A depicts an example beam map showing hopping groups away fromthe Equator.

FIGS. 20B depicts an example beam map showing hopping groups at theEquator.

FIGS. 21 is a table providing an example assignment of hopping groupsaway from the Equator.

FIGS. 22 is a table providing an example assignment of hopping groups atthe Equator.

FIG. 23 depicts an example beam map showing the Field of Regard,depicting a moment in time and graphically indicating which subset ofspot beams of the various hopping groups are active in the currentepoch.

FIG. 24 describes a portion of one example of a beam hopping plan.

FIG. 25 depicts timing for one embodiment of a super-frame.

FIG. 26 depicts content of one embodiment of a super-frame.

FIG. 27 depicts an example of a payload of a super-frame.

FIG. 28 depicts a portion of a satellite communication system, showingsample transmission times.

FIG. 29 is a flow chart describing one embodiment of a process forperforming time domain beam hopping with a constellation ofnon-geostationary satellites that can dynamically change beam hoppingplans.

FIG. 30 describes a portion of one example of a beam hopping plan, anddepicts time multiplexing of gateways.

FIG. 31 is a flow chart describing one embodiment of a process forperforming time domain beam hopping and time multiplexing gateways.

FIG. 32 is a flow chart describing one embodiment of a process forperforming time domain beam hopping on a satellite.

FIG. 33 depicts a portion of a satellite communication system, showing asatellite that is configured to implement a beam hopping plan thatduring a hopping period provides throughput to a first spot beam for anaggregated time duration based on bandwidth assignments to the firstgateway and the first set of subscriber terminals.

FIG. 34 is a flow chart describing one embodiment of a process forperforming time domain beam hopping, taking into account the bandwidthneeds of the subscriber terminal and the gateway.

FIG. 35 is a chart describing one example of sharing capacity bydividing up epochs or capacity units based on pro-rate bandwidth needs.

FIG. 36 depicts a portion of a satellite communication system, showing ahandover of a subscriber terminal between spot beams on a samesatellite.

FIG. 37 is a flow chart describing one embodiment of a gateway processfor performing a handover of a subscriber terminal between spot beams ona same satellite.

FIG. 38 is a flow chart describing one embodiment of a gateway processfor performing a handover of a subscriber terminal between spot beams ona same satellite.

FIG. 39 is a flow chart describing one embodiment of a subscriberterminal process for performing a handover of the subscriber terminalbetween spot beams on a same satellite.

FIG. 40 is a flow chart describing one embodiment of a subscriberterminal process for performing a handover of the subscriber terminalbetween spot beams on a same satellite.

FIG. 41 depicts a portion of a satellite communication system, showing ahandover of a subscriber terminal between spot beams of differentsatellites.

FIG. 42 is a flow chart describing one embodiment of a gateway processfor performing a handover of a subscriber terminal between spot beams ondifferent satellites.

FIG. 43 is a flow chart describing one embodiment of a subscriberterminal process for performing a handover of the subscriber terminalbetween spot beams on different satellites.

FIG. 44 depicts a portion of a satellite communication system, showingtwo cooperating gateways operating within hopping beams andcommunicating with hopping beams.

FIG. 45 is a flow chart describing one embodiment of a process forperforming a handover of gateways between satellites, where the gatewaysare operating within hopping beams and communicating with hopping beams.

FIGS. 46A, 46B, 46C, and 46D depict Fields of Regards of two satellitesmoving over coverage areas.

FIG. 47 depicts a portion of a satellite communication system, showing agateway connecting to steerable spot beams of two satellites forperforming a handover.

FIG. 48 is a flow chart describing one embodiment of a process forperforming a handover for gateways communicating with steerable spotbeams of the satellites in the constellation.

FIGS. 49A, 49B, 49C, 49D and 49E depict a Field of Regard of a satellitemoving over coverage regions as the satellite orbits the Earth.

FIG. 50 is a flow chart describing one embodiment of a process forperforming timing synchronization for the satellite communicationsystem.

FIG. 51 is a flow chart describing one embodiment of a process forsynchronizing a gateway to a satellite.

FIG. 51A depicts an example beacon signal.

FIG. 52 is a flow chart describing one embodiment of a process forsynchronizing a subscriber terminal to a gateway.

FIG. 53 is a flow chart describing one embodiment of a process performedby gateways to automatically determine a location of a satellite.

DETAILED DESCRIPTION System Overview

A satellite communication system is proposed that comprises aconstellation of non-geostationary satellites orbiting the Earth, aplurality of gateways and a plurality of subscriber terminals (alsoreferred to as terminals). The subscriber terminals communicate with thegateways via the satellites, as the satellites move in orbit. Each ofthe satellites provide a plurality of non-articulated spot beams thatimplement time domain beam hopping and a plurality of steerable spotbeams for communicating with the gateways and subscriber terminals. Thesystem can be used to provide access to the Internet or other network,telephone services, video conferencing services, private communications,broadcast services, as well as other communication services.

Synchronization technology is implemented for a satellite communicationsystem. Master clock information is accessed at a terrestrial location.A timing message based on the master clock information is transmittedfrom the terrestrial location to a satellite as the satellite is inorbit. The satellite is synchronized to the master clock based on thetiming message. A beacon signal is transmitted from the satellite towardEarth. The beacon signal includes timing information. The beacon signalis received at a ground based gateway. The gateway is synchronized tothe satellite based on the beacon signal. Communication is sent from thegateway to a terminal via the satellite. The communication includestiming data. The terminal is synchronized to the gateway based on thetiming data.

FIG. 1 is a block diagram depicting a portion of a satellitecommunications system that includes one or more satellites. FIG. 1depicts satellite 201, which is a non-geostationary satellite. Ageostationary satellite moves in a geosynchronous orbit (having a periodof rotation synchronous with that of the Earth's rotation) in the planeof the Equator, so that it remains stationary in relation to a fixedpoint on the Earth's surface. This orbit is often achieved at analtitude of 22,300 miles (35,900 km) above the earth; however, otheraltitudes can also be used. A non-geostationary satellite is a satellitethat is not a geostationary satellite and is not in an orbit that causesthe satellite to remain stationary in relation to a fixed point on theEarth's surface. Examples of non-geostationary satellites include (butare not limited to) satellites in Low Earth Orbits (“LEO”), Medium EarthOrbits (“MEO”) or Highly Elliptical Orbits (“HEO”). Although FIG. 1 onlyshows one satellite, in some embodiments (as described below) the systemwill include multiple satellites that are referred to as a constellationof satellites.

In one embodiment, satellite 210 comprises a bus (i.e., spacecraft) andone or more payloads, including a communications payload. The satellitemay also include multiple power sources, such as batteries, solarpanels, and one or more propulsion systems, for operating the bus andthe payload. The satellite includes an antenna system that provides aplurality of beams, including non-articulated and steerable spot beams,for communicating with subscriber terminals and gateways.

A subscriber terminal is a device that wirelessly communicates with asatellite, usually to be used by one or more end users. The termsubscriber terminal may be used to refer to a single subscriber terminalor multiple subscriber terminals. A subscriber terminal is adapted forcommunication with the satellite communication system includingsatellite 201. Subscriber terminals may include fixed and mobilesubscriber terminals including, but not limited to, a cellulartelephone, wireless handset, a wireless modem, a data transceiver, apaging or position determination receiver, or mobile radio-telephone, acellular backhaul, a trunk, an enterprise computing or storage device,an airborne device, a maritime device or a head end of an isolated localnetwork. A subscriber terminal may be hand-held, portable (includingvehicle-mounted installations for cars, trucks, boats, trains, planes,etc.) or fixed as desired. A subscriber terminal may be referred to as awireless communication device, a mobile station, a mobile wireless unit,a user, a subscriber, a terminal or a mobile.

The term gateway may be used to refer to a device that communicateswirelessly with a satellite and provides an interface to a network, suchas the Internet, a wide area network, a telephone network or other typeof network. In some embodiments, gateways manage the subscriberterminals.

FIG. 1 also shows a Network Control Center 230, which includes anantenna and modem for communicating with satellite 201, as well as oneor more processors and data storage units. Network Control Center 230provides commands to control and operate satellite communication payload201, as well as all other satellite communication payloads in theconstellation. Network Control Center 230 may also provide commands toany of the gateways (via a satellite or a terrestrial network) and/orsubscriber terminals.

In one embodiment, satellite 201 is configured to provide two hundredfixed (i.e., non-articulated so that they are fixed in relation tosatellite 201) spot beams that use time domain beam hopping among thespot beams. In other embodiments, more or less than two hundred spotbeams can be used for the time domain beam hopping. In one embodiment,the two hundred hopping beams are divided into thirty six hopping groupssuch that one beam in each group is active at a given time; therefore,thirty six of the two hundred spot beams are active at an instance intime. In addition to the two hundred non-articulated spot beams thatperform time domain beam hopping, one embodiment of satellite 201includes eight 4.2 degree steerable spot beams used to communicate withgateways. In other embodiments, more or less than eight can be used.Additionally, satellite 201 includes six 2.8 degree steerable spot beamswhich can have a dual purpose of communicating with gateways and/orproviding high capacity communication for subscriber terminals thatwould otherwise fall under the hopping beams of the two hundred spotbeams performing time domain beam hopping. Other embodiments can usedifferent sized spot beams.

For example purposes only, FIG. 1 shows five spot beams: 202, 206, 210,214 and 218. Spot beam 202 is a 4.2 degree steerable spot beam thatilluminates coverage area 204 for communicating with one or moregateways 205 via downlink 202 d and uplink 202 u. Spot beam 206 is a 2.8degree steerable dual purpose beam that illuminates coverage area 208 inorder to communicate with one or more gateways 209 and one or moresubscriber Terminals ST via downlink 206 d and uplink 206 u. Spot beam210 is a 2.8 degree steerable spot beam that could be used tocommunicate with gateways and/or subscriber terminals ST, but in theexample of FIG. 1 spot beam 210 illuminates coverage area 212 tocommunicate with one or more gateways 213 via downlink 210 d and uplink210 u. The two hundred spot beams that perform time domain beam hoppingcan be used to communicate with subscriber terminals and/or gateways.Spot beams 214 and 218 are two examples of the two hundrednon-articulated spot beams that performed time domain beam hopping. Spotbeam 214 illuminates coverage area 216 to communicate with one or moregateways 217 and one or more subscriber terminals ST via downlink 214 dand uplink 214 u. Spot beam 218 illuminates coverage area 220 tocommunicate with subscriber terminals ST via downlink 218 d and uplink218 u.

FIG. 2 is a block diagram depicting more details of one embodiment of anantenna system of satellite 201. For example, FIG. 2 shows antennas 252,254, 258 and 260 which provide the two hundred spot beams that implementtime domain beam hopping. Each of antennas 252, 254, 258 and 260 providefifty spot beams each. FIG. 2 shows feed cluster 262 pointed at antenna252, feed cluster 264 pointed at antenna 254, feed cluster 266 pointedat antenna 258 and feed cluster 268 pointed at antenna 260.Additionally, satellite 201 includes six 2.8 degree steerable antennasfor communicating with gateways and/or providing high capacity beams forsubscriber terminals, including antennas 286, 288, 290, 292, 294 and296. Satellite 201 also includes eight 4.2 degree steerable antennas forcommunicating with gateways, including antennas 270, 272, 274, 276, 278,280, 282 and 284. In one embodiment, the antennas are mechanicallysteerable. In another embodiment, a phased array or other means can beused to electronically steer the spot beams. Satellite 201 also includesan antenna 298 for communicating with network control center 230 inorder to provide telemetry and commands to satellite 201, and providestatus and other data back to network control center 230.

Antenna 298, or any of the other antennas, can also be used to provide abeacon signal. In some embodiments, satellite 201 can include anadditional antenna for providing the beacon signal. In traditionalsatellites, the beacon signal provides subscriber terminals and gatewayswith a gauge to determine how much power should be used. A terminal onthe ground can transmit a signal which the satellite will use togenerate a corresponding downlink, which can then be compared to thestrength of the beacon signal, and then can adjust its power up or downto match the beacon signal. The beacon signal can also be used todetermine when a satellite is not operational. Additionally, beaconsignals can be used to compensate for Doppler shift. Since the terminalsknows the beacon is supposed to be on a certain frequency, it cancalculate its Doppler based on the current reception of the beaconsignal.

FIG. 3 provides an example beam map for the two hundred non-articulatedspot beams of satellite 201 that implement time domain beam hopping. Inone embodiment, those spot beams are fixed in direction, relative tosatellite 201. As can be seen, the two hundred spot beams depicted inFIG. 3 are numbered 1-200. In one embodiment, the spot beams overlap;for example, the −5 dB contour of each spot beam overlaps with the −5 dBcontour of other spot beams neighboring it. All the spot beams togethercomprise the Field of Regard of satellite 201. The Field of Regard ofthe satellite is different than the Field of View of the satellite. Forexample, the Field of Regard is the target area that the satellite cansee/communicate based on its position. Thus, the entire beam map of FIG.3 is the Field of Regard. In contrast, the Field of View is the areathat the satellite's payload can actually see at an instance in time.For example, when performing time domain beam hopping, only a subset ofthose spot beams depicted in FIG. 3 are active at a given time.Therefore the Field of View is less than the Field of Regard.

In one embodiment, satellite 201 is only one satellite of a largerconstellation of satellites that implement the satellite communicationsystem. In one example embodiment, the satellite constellation includeseleven satellites, with each satellite having the same structure assatellite 201. However, each of the satellites can be independentlyprogrammed to implement the same or different time domain beam hoppingplans, as will be explained below. FIG. 4 is a map of the world showingeleven MEO satellites 302, 304, 306, 308, 310, 312, 314, 316, 318, 320,and 322. In one embodiment, all eleven satellites are in orbit about theEquator. In one example, all eleven satellites are moving in the sameorbital direction along the same orbital path and are equally spacedapart from each other. Because the satellites are in MEO orbit, they arenon-geostationary, meaning that they will move with respect to anylocation on the Earth. As the satellites move in orbit, the user andgateway spot beams' coverage areas will drift across the Earth's surfacewith the satellites. In one example, there will be a drift rate of 360degrees longitude every six hours, or one degree per minute. In suchembodiment, each satellite will orbit past the same earth position insix hours, or four times a day. In one embodiment, the time it takes todrift the width of a spot beam covering subscriber terminals (one of thetwo hundred beam hopping spot beams) is approximately 2.8 minutes (168seconds).

FIG. 5 shows the same map of the world as FIG. 4, with the beam maps(the Field of Regard) for each of the satellites depicted over the map.For example, satellite 302 projects beam map 350, satellite 304 projectsbeam map 352, satellite 306 projects beam map 354, satellite 308projects beam map 356, satellite 310 projects beam map 358, satellite312 projects beam map 360, satellite 314 projects beam map 362,satellite 316 projects beam map 365, satellite 318 projects beam map366, satellite 320 projects beam map 368, and satellite 322 projectsbeam map 370. Note that the satellites 302-322 are constantly movingwest to east; therefore, beam maps 350-370 are also moving west to east,and are never stationary (in one embodiment). As can be seen, adjacentsatellites have adjacent beam maps and adjacent Fields of Regard whenoperating the satellites. In one embodiment, the beam maps of adjacentsatellites overlap so that among the constellation's satellites there iscontinuous coverage around the globe; however, there may be gaps incoverage at the north and south poles (where there is little demand).That is, the beam map of each satellite is adjacent to a beam map on theadjacent satellite to provide a composite beam map that circumnavigatesthe Earth.

FIG. 6 is a block diagram of one embodiment of a communications payloadfor non-geostationary satellite 201. In one embodiment, each ofsatellites 302-322 implement the same structure and design of satellite201; therefore, the payload of FIG. 6 will be implemented on each ofsatellites 302-322. Traditionally, the communications path from thegateway to the subscriber terminal via the satellite is referred to asthe forward path and the communications path from the subscriberterminals to the gateway via the satellite are referred to as the returnpath. When a satellite is used to provide connectivity to the Internet,a user at a computer connected to a subscriber terminal will send arequest for content on the Internet to the gateway via the satellite,and the gateway will provide, in response to that request, access ontothe Internet. The response from the Internet will be provided to thegateway, and then forwarded onto the subscriber terminal via thesatellite.

The structure of FIG. 6 implements both the forward path and the returnpath. The uplink beams are received at the left hand portion of thecomponents of FIG. 6 and the downlink beams are provided at the righthand edge of the components of FIG. 6. For example, FIG. 6 shows eightgateway steerable dual polarization antennas 400 and six gateway/highcapacity subscriber terminal steerable antennas with dual polarization402 for receiving uplink beams. FIG. 6 also shows the two hundrednon-articulated spot beams divided into two groups: one hundred andseventy spot beams 404 illuminating areas away from the Equator andthirty spot beams 406 illuminating areas at the Equator.

The eight 4.2 degree gateway steerable spot beams 400 provide sixteensignals, eight in each polarization (left hand/right hand orhorizontal/vertical). Six of those sixteen signals are provided toselection matrix 410 which includes a set of switches that selects twoof the six input signals and provides those two selected signals to lownoise amplifier 412. Ten of the 16 dual polarization signals fromantennas 400 are applied directly to low noise amplifier bank 412comprising low noise amplifiers. Note that the antennas 400 of FIG. 6correspond to antennas 270-284 of FIG. 2. Similarly, antennas 402 ofFIG. 6 correspond to antennas 286-296 of FIG. 2. The six gatewaysteerable antennas 402 provide 12 signals (six signals in twopolarizations). Six of those signals are provided directly to low noiseamplifier bank 412, the other six signals are provided to a 6:2selection matrix 414, which chooses two of the signals to provide to lownoise amplifier bank 412. Note that the satellite payload will include aprocessor (not depicted) which controls each of the selection matricesdescribed herein. Alternatively, satellite bus will include a processorthat will control the selection matrices. As described above, low noiseamplifier bank 412 has 20 input signals and, therefore has 20 outputsignals. Fourteen of the signals output from low noise amplifier bank412 are provided to separate splitters 416. That is, there are 14splitters 416. Each splitter splits the incoming signal into four copiesnoted as: F1/3, F2/4, F5/6 and F7/8. The other six outputs from LNA 412are provided to a different set of splitters 418 that split the signalto four copies labeled as: F1/3, F2/4, F7/8 and R-HC. The seven outputsof the splitter that started with an F are part of the forward path. Theone output of the splitter 418 that is labeled R-HC is part of thereturn path from a steerable high capacity spot beam used to connect tosubscriber terminals. In one embodiment splitters 416 and 418 includefilters for passing the frequency bands of the labeled output andstopping all other frequencies.

After the splitters 416 and 418, the signals are sent to appropriatematrices 420, 422, 424, 426 and 428 in order to select which bands touse. Selection matrix 420 receives the signal F1/3. Selection matrix 422receives signal F2/4. Selection matrix 424 receives signal F5/6.Selection matrix 426 receives signal R-8C. Selection matrix 428 receivesF7/8. Eleven signals of the output of selection matrix 420 are providedto down converter 440, which provides its output to channel 442. The 11signals of the output of selection matrix 422 are provided to downconverter 444, which provided its output to channelizer 442. The outputof selection matrix 424 includes seven signals that are provided to downconverter 446, which provides its output to channelizer 442. The outputof selection matrix 426 includes six signals that are provided to downconverter 446, which provides its output to channelizer 442. The outputof selection matrix 428 includes 11 signals that are provided to downconverter 448, which provides its output to channelizer 442. Each of theselection matrices includes a series of programmable switches to route asubset of inputs to the output ports.

The one hundred and seventy non-Equatorial spot beams 404 are providedto selection matrix 443 which chooses twenty eight out of the onehundred and seventy spot beams. That is, one beam from each of 28 beamhopping groups (discussed below) is chosen. Those 28 signals are sent tolow noise amplifier 444. Half of the signals output from low noiseamplifier 444 are provided to splitters 446. The other half of thesignals are provided to splitters 448. Each of the fourteen splitters446 make three copies of the signal and output those three copies asF1/3, F2/4 and RTN. Each of the fourteen splitters 448 make three copiesof their respective incoming signals and output them F5/6, F7/8 and RTN.Note that the signals F1/3, F2/4, F5/6 and F7/8 are part of the forwardpath representing communication from a gateway in one of the one hundredand seventy hopping beams. The signal RTN is part of the return path,from subscriber terminals. Note that in some embodiments, each of thesplitters has appropriate band pass filters. In some embodiments, eachof the selection matrices has appropriate band pass filters atrespective inputs and/or outputs.

FIG. 6 shows the thirty non-articulated beam hopping spot beams near theEquator being provided to selection matrix 454. The eight selectedsignals are provided to low noise amplifier 456 which outputs a signallabeled RTN. Note in some embodiments, each of the low noise amplifiers456, 444 and 412 have band pass filters at their input and/or output.Additionally, band pass filters can be used at each of the antennas 400,402, 404 and 406. Based on the output of splitters 448 and low noiseamplifier 456, thirty six signals labeled RTN are frequency combined inMUX 450 which outputs 9 signals. The output of MUX 450 is provided todown converter 452. The output of down converter 452 is provided tochannelizer 442. Each of the selection matrices 410, 414, 420, 422, 424,426, 428, 443 and 454 includes switches that are used to switchthroughput among the various spot beams in the hopping groups or amongvarious bands from the gateways and high capacity steerable spot beams.The chosen signals are provided to channelizer 442 which is used toroute spectrum between the uplinks and downlinks. In one embodiment,channelizer 442 is a digital channelizer that is fully programmable inorbit. More details of channelizer 442 are provided below with respectto FIG. 7. Channelizer 442 can be thought of as a giant switching orrouting matrix that is fully programmable. FIG. 6 shows that channelizer442 provides fourteen outputs to upconverter 460, fourteen outputs toupconverter 472, eight outputs to upconverter 480, eight outputs toupconverter 490 and twenty outputs to upconverter 502. Note thatupconverters 460, 472, 480 and 490 (all which function to increase thefrequency of the signal) are provided as part of the forward path, whileupconverter 502 is provided for the return path. The output of each ofthe 14 up converters 460 are provided to filters 462. The output of eachof the fourteen filters 462 are provided to solid state power amplifiers(SSPA) 464. The output of each of the fourteen SSPAs are provided tomultiplexer 466. The output of multiplexer 466 is provided to 28:170selection matrix 468. The 170 outputs of selection matrix 468 areprovided as the one hundred and seventy non-Equatorial non-articulatedbeam hopping spot beams 470.

The output of the fourteen upconverters 472 are provided to separatefilters 474. The output of each of the fourteen filters 474 is providedto separate SSPAs 476. The output of each of the fourteen SSPAs 476 areprovided to multiplexer 478. The output of multiplexer 478 is providedto selection matrix 468. The output of the eight upconverters 480 areprovided to filters 482. The output of the eight filters 482 areprovided to separate SSPAs 484. The output of SSPAs 484 are provided toselection matrix 486. The output of selection matrix 486 is provided asthe thirty Equatorial region non-articulated beam hopping spot beams of488. Note that the SSPAs can be turned off (e.g., when the satellite isover the ocean or other non-inhabited area) to conserve power.

The output of upconverters 490 (which can be part of the forward path orthe return path) are provided to filters 492. The output of the eightfilters 492 are provided to SSPAs 494. The output of the eight SSPAs 494are provided to selection matrix 496. The 12 output signals fromselection matrix 496 are provided to multiplexor 498. The output ofmultiplexor 498 are provided as the six 2.8 degree gateway/high capacitysubscriber terminals steerable spot beams, with dual polarization.

The output of upconverters 502 are provided to separate filters 504. Theoutput of the twenty filters 504 are provided to separate SSPAs 506. Theoutput of the 20 SSPAs 506 are provided to selection matrix 508, whichprovides 42 outputs. Twelve of the 42 outputs are provided tomultiplexer 498, fourteen of the 42 outputs are provided to multiplexer466 and multiplexer 478, and sixteen of the 42 outputs are provided asthe eight gateway steerable dual polarization spot beams describedabove.

In an alternative embodiment, many or all of the selection matrices canbe eliminated by having the selection/switching performed by channelizer442. In some embodiments, the payload of FIG. 6 can be fully implementedby just a channelizer that will switch, route and filter.

FIG. 7 is a block diagram describing one example implementation ofchannelizer 442. The technologies described herein are limited to anyone particular architecture or implementation of channelizer 442. Theembodiment of FIG. 7 is only one example that is suitable for thetechnology described herein and many other configurations are alsousable. Inputs to channelizer 442 are provided to a receive module 550,where signals can be filtered, amplified, stored or simply received. Theoutput of receive module 550 is provided to switch network and beamforming network 552. The output of switch network and beam formingnetwork 552 is provided to a transmission module 554 which provides theoutputs of channelizer 442. Channelizer 442 also includes an auxiliarymodule 556, control unit 558 and clock generator 560, which are allconnected to receive module 550, switch network/beam forming network 552and transmission module 554. In one embodiment, control unit 558includes one or more processors used to program the switch networks/beamforming network 552. Clock generator 560 provides a clock signal toimplement timing within channelizer 442. In one embodiment, auxiliarymodule 556 is used to control the switches of the switching network,adjust beams, provide spectrum analysis and provide uplink and downlinkmodems.

In one embodiment, each of the non-geostationary satellites 302-322 areconfigured to provide a plurality of spot beams (described above) thatimplement a first frequency plan at the Earth's Equator and a secondfrequency plan away from the Earth's Equator, with the first frequencyplan being different than the second frequency plan. Thus, whenoperating the constellation of non-geostationary satellites, multiple orall of those satellites within the constellation will communicate with aterminal or multiple terminals at the Equator using spot beams toimplement the first frequency plan and multiple or all of the satellitesof the constellation will communicate with a different terminal(s) thatis away from the Equator using spot beams that implement the secondfrequency plan.

In one embodiment, the frequency plans at the Equator and away from theEquator are both using the KA band; however, other bands can also beused. FIGS. 8 and 9 provide the frequency plan for the areas away fromthe Earth's Equator, while FIGS. 11 and 12 provide the frequency planfor the areas at the Equator. More specifically, FIG. 8 provides thefrequency plan away from the Equator for uplinks. FIG. 8 shows theuplink using between 27.50 GHz through 30.00 GHz. The frequency planincludes three components. The first component is the forward uplinkutilized by gateways including eight colors (frequency band pluspolarization) each comprising a 500 MHz frequency band in onepolarization (left hand circular polarization LHCP or right handcircular polarization RHCP) labeled as FWD1 UL, FWD2 UL, FWD3 UL, FWD4UL, FWD5 UL, FWD6 UL, FWD7 UL, FWD8 UL. The second component of FIG. 8includes the return path used by subscriber terminals which includeseight colors each of which is a frequency band of 100 MHz in onepolarization labeled as R1, R2, R3, R4, R1 a, R2 a, R3 a, and R4 a. FIG.8 also shows frequency plan for the return path used by subscriberterminals in the high capacity steerable beams which comprise fourcolors each of which is a frequency band of 225 MHz and one polarization(LHCP or RHCP), labeled as R1 HC UL, R2 HC UL, R3 HC UL and R4 HC UL.The arrow labeled TC indicates the frequency assigned for Telemetry andControl signals.

FIG. 9 shows the frequency plan for the downlink in the regions awayfrom the Equator. The frequency plan for communicating downlink beam tothe subscriber terminals uses four colors each with a 500 MHz frequencyband in one polarization (LHCP or RHCP) labeled as FWD D1 DL, FWD D2 DL,FWD D3 DL and FWD D4 DL. As mentioned above, the 170 non-articulatedspot beams that implement time domain beam hopping can also servegateways and do so using four colors each of which are 180 MHz frequencybands in one polarization and labeled in FIG. 9 as R1 FB DL, R2 FB DL,R3 FB DL and R4 FB DL. As discussed above, the satellite can includehigh capacity steerable beams that can service both gateways andsubscriber terminals. The downlink to the subscriber terminals in thosehigh capacity steerable beams use four colors each with 400 MHzfrequency band in one polarization that are labeled in FIG. 9 as FWD HC1DL, FWD HC2 DL, FWD HC3 DL, and FWD HC4 DL. As discussed above, thesatellite can include 4.2 degree steerable spot beams that communicatewith gateways. Those beams will utilize two colors, each which includes400 MHz frequency band in one polarization and composed of 8 subchannels that are labeled in FIG. 9 as R1, R2, R3, R4, R1 a, R2 a, R3and R4 a. When the high capacity steerable beams are utilized, thedownlink can also be part of the 4.2 degree steerable spot beams returnpath and includes a 225 MHz frequency band in one polarization, withinthe 400 available spectrum and labeled R1/2/3/4 HC DL. Note that in oneembodiment, frequency plan for the uplink and the downlink areconstructed such that the subscriber terminals and the gateways usedifferent frequencies. When a particular spot beam of the of spot beamsperforming time domain beam hopping serves a gateway and subscriberterminals then the subscriber terminals and the gateway use differentfrequencies. The arrow labeled TM (which can be in-band or out of band)represents Telemetry and Control Signals. Note that while the exampleembodiment depicted in FIGS. 8 and 9 shows the two polarizations as lefthand circular polarization LHCP or right hand circular polarizationRHCP, other embodiments can use left hand or right hand polarizationswhet her it is circular of linear. Some embodiments of satellitecommunication systems use vertical and horizontal polarization.

FIG. 10 is a beam map that shows the same Field of Regard as FIG. 3,and, therefore, the same beam map as FIG. 3. However, instead of showingnumbers in each of the spot beams on the beam map, FIG. 10 shades eachbeam. The shading of FIG. 10 corresponds to the shading in FIG. 9. Thus,each of the spot beams is assigned a downlink color (frequency band andpolarization) using the frequency plan of FIG. 9. For example, thebottom left hand most beam in row one has vertical shading and thereforecorresponds to FWD D3 DL and the uppermost right hand beam in row 22 hasangled shading which corresponds to FWD D1 DL. FIG. 10 shows a fourcolor reuse plan.

FIGS. 11 and 12 show the frequency plan for the area at the Equator. Inone embodiment, different frequency plans are used at the Equatorbecause there is a need to avoid interference with geostationarysatellites. FIG. 11 depicts the frequency plan for the uplink. In oneembodiment, none of the steerable spot beams will be used in the areanear the Equator. Therefore, the area near the Equator will only beserviced by non-articulated spot beams that are implementing time domainbeam hopping. The uplink in the Equator area will include eight colors,each of which has a frequency band of 100 MHz in one polarization sothat four colors are left hand polarized and between 28.60 GHz and 29.10GHz. The eight colors of the uplink in the Equator region are labeled asR1, R2, R3, R4, R1 a, R2 a, R3 a, and R4 a. Each of these frequencybands are used as part of the return path implementing communicationfrom subscriber terminals toward the satellite.

FIG. 12 shows the frequency plan for the downlink in the area of theEquator and represents four colors used for the forward downlink. Eachof the colors includes frequency bands that are 250 MHz in onepolarization, labeled as FWD E1, FWD E2, FWD E3, and FWD E4. The fourcolors range between 18.80 GHz and 19.3 GHz.

So differences in the downlink at the Equator versus away from theEquator includes away from the non-Equator downlink colors having twiceas big frequency ranges. For example, FWD D1 DL is 500 MHz between 18.8and 19.3 GHz versus FWD E1 being 250 MHz between 18.8 and 19.05. FWD D2DL is 500 MHz between 19.3 and 19.8 GHz versus FWD E2 being 250 MHzbetween 19.05 GHz and 19.3 GHz; FWD D3 DL is 500 MHz between 18.8 and19.3 GHz while FWD E3 is 250 MHz between 18.8 and 19.05 GHz; and FWD D4DL is 500 MHz between 19.3 and 19.8 GHz versus FWD E4 being 250 MHzbetween 19.05 and 19.3 GHz. While the return links in the Equator andnon-Equator are both 100 MHz bands, the frequency bands for the Equatorregion are shifted up in frequency; for example, R1 in FIG. 8 starts at28.54 GHz while R1 in FIG. 11 starts at 28.6 GHz.

As can be seen from FIGS. 8, 9, 11 and 12, the frequency plan away fromthe Equator includes frequency ranges not in the frequency plan at theEquator; the frequency plan at the Equator includes different uplinkfrequency ranges than the second frequency plan; the frequency plan awayfrom the Equator includes larger frequency ranges than frequency plan atthe Equator; the frequency plan away from the Equator includes morefrequency ranges than the frequency plan at the Equator; and thefrequency plan away from the Equator includes more bandwidth than thefrequency plan at the Equator. The spot beams at the Equator consist ofonly non-articulated spot beams relative to the satellite and the spotbeams away from the Equator include non-articulated spot beams relativeto the satellite and steerable spot beams.

When operating the constellation of non-geostationary satellites302-322, multiple satellites of the constellation communicating with afirst terminal at the Equator use spot beams that implement thefrequency plan for the Equator and multiple satellites of theconstellation communicating with a second terminal away from the Equatoruse spot beams that implement the frequency plan for regions away fromthe Equator (e.g., using adjacent Fields of Regard for the satellites ofthe constellation).

FIG. 13 shows the same Field of Regard and same beam map as FIG. 3 andFIG. 10; however, FIG. 13 graphically depicts the Equator zone and thenon-Equator zone (away from the Equator). With the Equator zonecorresponds to the frequency plan of FIGS. 11 and 12 and the non-Equatorzone corresponds to the frequency plan of FIGS. 8 and 9. Note that FIG.13 uses shading for the Equator zone. If the rows of the beams in thebeam map of FIGS. 3, 10 and 13 were to be numbered, as depicted in FIGS.10 and 13, rows 10, 11 and 12 refer to the Equator zone. Note that FIG.12 uses shading for the four colors of the frequency plan. This shadingis also used to assign each of the colors to the various spot beams inthe Equator zone as depicted in FIG. 10.

FIG. 13A is flowchart describing one embodiment of a process foroperating a constellation of satellites that use different frequencyplans and different hopping plans (described below) between spot beamsat the Equator and spot beams away from the Equator. In step 580, thesystem operates the constellation of non-geostationary satellites in anorbit at the Equator. In other embodiments, other orbits can be used. Instep 582, each satellite of the constellation provides a first set ofspot beams that illuminate a region over the Equator using a frequencyplan for the Equator, for example, the frequency plan of FIGS. 11 and12. In step 584, each satellite of the constellation provides a secondset of spot beams that illuminates a region away from the Equator usinga frequency plan for non-Equatorial areas. For example, step 584 caninclude using the frequency plans of FIGS. 8 and 9 in the non-Equatorzone of FIG. 13. Step 582 can include using the frequency plans of FIGS.11 and 12 in the Equator zone of FIG. 13. In step 586, each of thesatellites of the constellation flies over a terminal at or near theEquator as it is traversing along its orbital path along the Equator. Asit flies over that terminal, it communicates with that terminal usingthe first set of spot beams and the frequency plan for the Equator. Instep 588, as each satellite of the constellation flies over a terminalin a region away from the Equator, it communicates with that terminalusing the second set of spot beams and the frequency plan fornon-Equatorial areas (e.g., the non-Equator zone). As discussed above,each of the 11 satellites of the example constellation depicted in FIG.4 traverse over the same orbit four times a day and thus each of thesatellites will have an opportunity to communicate with each terminalpotentially four times a day (if that terminal is stationary and alwayson), using the appropriate Equator zone or non-Equator zone frequencyplan. The process of FIG. 13A is not necessarily performed in the orderor sequence depicted in FIG. 13A, and other sequences can beimplemented. For example, step 580 can be thought of as summarizing thewhole operation of the system and can encompass all other steps, steps582 and 584 can be performed in parallel, and steps 582 and 584 can beperformed in parallel.

As discussed above, the high capacity steerable beams can provideservice to subscriber terminals as well as gateways. The satellites cansupport full mesh networks between subscribers terminals in highcapacity steerable beams. For example, two subscriber terminals in asame high capacity steerable beam can communicate with each otherdirectly via the satellite without going through a gateway.Additionally, two subscriber terminals in a different high capacitysteerable beams can communicate with each other directly via thesatellite without going through a gateway. These subscriber terminals inhigh capacity steerable beams and the high capacity steerable beams arenot performing time domain beam hopping. Additionally, gateways cancommunicate with subscriber terminals in the high capacity beams withoutusing time domain beam hopping. Another embodiment is to configure beamassignments in the articulated array such that continuous connectivityis provided to geographic locations, such that no beam hopping isrequired by either the gateway or subscriber terminals in either feederof subscriber uplinks.

Single Polarity Across Path of Spot Beams

As the 11 satellites 302-322 travel along their orbital path west toeast at the Equator, the spot beams (including the entire Field ofRegard) will move over the Earth's surface from west to east. As thespot beams move over a subscriber terminal, that subscriber terminalwill first connect with an eastern spot beam in the Field of Regard andthen slowly move towards the western spot beams as the spot beams as awhole (see FIG. 3) move west to east. For example, a subscriber terminalmay first connect to spot beam 199. Subsequently, the subscriberterminal will move through spot beams 129, 130, 131, 132, 133, 134, 135,136 and then 137.

In one embodiment, each of the non-geostationary satellites 302-322provide the plurality of spot beams (e.g., the beam map in Field ofRegard of FIG. 3) to use multiple frequencies and multiple (e.g., two)polarities, such that all spot beams along a path completely across theplurality of spot beams in the orbital direction communicate using acommon polarization. In the above-described example, the path completelyacross the plurality of spot beams was from spot beam 199 to spot beam137. That path is in the orbital direction because the satellite istraveling west to east along the Equator. In this embodiment, all thespot beams in the path across beams 199, 129, 130, 131, 132, 133, 134,135, 136 and 137 are configured to have the same polarity. This way, asthe Field of Regard travels over and past a subscriber terminal, thatsubscriber terminal will not need to change polarities as it hands overbetween spot beams or between satellites. It may be that the subscriberterminal may have to change frequencies when it changes spot beams butit will not need to change polarities. This is more graphically depictedin FIG. 14A which shows a Field of Regard (or a portion of a Field ofRegard), including a polarity of spot beams. In each spot beam, there isan L or an R to indicate whether the spot beam has left handpolarization or right hand polarization. Arrow 573 depicts a pathcompletely across the plurality of spot beams in the orbital directionand shows an example of how that path will only traverse across spotbeams having left hand polarization.

FIG. 14B shows another embodiment of a plurality of spot beams where thepath completely across the plurality of spot beams in the orbitaldirection is on a diagonal, as indicated by arrow 575. Arrows 573 and575 of FIGS. 14A and 14B indicate the path that a subscriber terminalwill take as the subscriber terminal is stationary and the spot beamstraverse over or pass the subscriber terminal. Note that the technologydescribed herein can be used with equatorial orbits and non-equatorialorbits (orbits that do not follow the equator), including ellipticalorbits.

FIGS. 15A-F provides another example of a subscriber terminal traversingcompletely across the plurality of spot beams in the orbital directionusing a single polarization. For example, in FIG. 15A, spot beams 1-11are depicted. Next to each spot beam number is an L or an R indicatingwhether it is left hand polarization or using right hand polarization.The initial position of the subscriber terminal is indicated by “S.” Asseen in FIG. 15A, the Field of Regard is due west of the subscriberterminal S. As also seen in FIG. 8, each spot beam is configured tocommunicate in at least one frequency range and one polarity.Polarizations are assigned to the spot beams such that all spot beamsthat illuminate and are configured to communicate with the subscriberterminal S on a ground location use a same polarity, while other spotbeams in the Field of Regard that do not illuminate subscriber terminalS can use another polarity. For example, FIGS. 15B-F shows the Field ofRegard moving west to east. In FIG. 15B, the Field of Regard has movedsuch that subscriber terminal S is now within spot beam 7 andcommunicating with spot beam 7 using right hand polarization. Meanwhile,spot beams 1, 2, 3 and 8-11 communicate with other subscriber terminalsusing left hand polarization. In FIG. 15C, the Field of Regard has movedsuch that the subscriber terminal S is communicating with spot beam 6,also using right hand polarization. In FIG. 15D, the Field of Regard hasmoved such that subscriber terminal S is not in communication with spotbeam 5, using right hand polarization. In FIG. 15E, the Field of Regardhas moved such that subscriber terminal S is in communication with spotbeam 4, using right hand polarization. In FIG. 15F, the Field of Regardhas moved east of subscriber terminal S and therefore subscriberterminal S is no longer in communication with any of the spot beams orthe Field of Regard depicted in FIG. 15F. As can be seen, as the spotbeams traversed across or past subscriber terminal S, subscriberterminal S continued to only communicate using right hand polarization.In one embodiment, each spot beams 4, 5, 6 and 7 use different frequencybands. In other embodiments, spot beams 5 and 7 can use the samefrequency band, and spot beams 4 and 6 can use the same frequency band.Therefore, as the Field of Regard traverses over or passed thesubscriber terminal, the subscriber terminal will need to changefrequencies between spot beams but will not change polarizations. Notchanging polarization makes the handover process faster and allows thesubscriber terminal to be a simpler less expensive design.

FIG. 15G is a flowchart describing one embodiment of a process foroperating a subscriber terminal, including changing frequencies forsubscriber terminals without the need to change polarization as thesatellite moves with respect to the subscriber terminal. In step 602,the subscriber terminal communicates with the current satellite usingthe current spot beam at a current frequency and fixed polarizationwhile the current satellite moves in orbit. Step 602 is continued to beperformed until the subscriber terminal comes to the edge of the spotbeam. At that point a handover must take place to the next spot beam. Itis determined whether the next spot beam is in a new satellite or in thecurrent satellite (step 604). If not in a new satellite (therefore, inthe current satellite), then the subscriber terminal automaticallychange its communication frequency to a frequency used for the nextadjacent spot beam on the current satellite, with no change topolarization (step 606). The process will then continue at step 602.However, if the next adjacent spot beam is for a new satellite (step604), then in step 610, the subscriber terminal automatically changescommunication frequency to the frequency for the first spot beam on thenext satellite, with no change to polarization. Thus, even as thesubscriber terminal hands off from satellite to satellite, it will notneed to change polarization. Thus, the subscriber terminal will maintainone polarization across the path of spot beams even over multiplesatellites. In step 612, the subscriber terminal will establishcommunication with the next satellite and the next satellite will thenbecome the current satellite. After step 612, the process moves back tostep 602.

FIG. 15H is a flowchart describing one embodiment of a process foroperating a satellite communication system, including implementinghandovers between spot beams such that a subscriber terminal does notneed to change polarities for the handover. The process of FIG. 15H isperformed by a non-geostationary satellite orbiting the Earth that isconfigured to provide a plurality of spot beams in the Field of Regard,where the plurality of spot beams use multiple frequencies and multiplepolarities, each spot beam of the plurality spot beam is configured tocommunicate in at least one frequency range and polarity. The satellitewill communicate with a terminal using different spot beams and a commonpolarity while the terminal is within the Field of Regard as the firstnon-geostationary satellite moves relative to the Earth and the terminalchanges spot beams. For example, in step 640, the satellite willcommunicate with a subscriber terminal (ground or airborne location)using the current spot beam and the common polarity for the path thatthat subscriber terminal will take across the Field of Regard. In step642, it is determined whether the satellite has moved too far such thatthe subscriber terminal will no longer be in the current spot beam. Ifnot, the process will continue in step 640. If, however, the satellitehas moved too far such that the subscriber terminal is at the edge of aspot beam, it is next determined whether the subscriber terminal is atthe edge of the beam map (step 644). If the subscriber terminal is notat the edge of the beam map, then the subscriber terminal will be handedover to the next adjacent spot beam in the orbital direction that usesthe same common polarity in step 646. Subsequently, the process willcontinue in step 640. If, however, the subscriber terminal was at theedge of the beam map, then in step 648, the subscriber terminal will behanded over to a spot beam on the adjacent satellite, also using thesame common polarity that the subscriber terminal has been communicatingwith.

Beam Hopping

As described above, each of satellites 302-322 are non-geostationarysatellites configured to provide a plurality of spot beams using timedomain beam hopping among the spot beams. In one embodiment, time domainbeam hopping includes multiple spot beams sharing frequency bandwidth orthroughput such that different spot beams can use the same frequencybandwidth or throughput at different times because the shared bandwidthor throughput hops between spot beams with only a subset of spot beamsbeing active at a time. Thus, the satellite is configured to switchthroughput among spot beams in a same hopping group. The time domainbeam hopping allows the Field of Regard to be much bigger than withoutusing time domain beam hopping. That is, the satellite can have a muchwider coverage area.

One of the challenges of time domain beam hopping with anon-geostationary satellite is that the coverage area is constantlychanging. In addition, over time demand for services changes. Thus thereare two changing variables demand and coverage area, which complicatesthe task of designing a non-geostationary satellite communicationsystem.

To implement the time domain beam hopping, the two hundrednon-articulated spot beams of the satellite are divided up into beamhopping groups. Each beam hopping group includes multiple spot beams. Atany instance in time, only one beam (or a subset of one or more beams)of a hopping group will be active, while the other beams of the hoppinggroup will be inactive. In one embodiment, all beams of the hoppinggroup utilize the same frequency and polarization. In anotherembodiment, the beams of a hopping group use the same frequency but mixpolarizations. The system will create the notion of a hopping perioddivided into a number of intervals called epochs. Each beam will beassigned one or more epochs during the hopping period. By assigningdifferent numbers of epochs to different spot beams allows the dwelltime to vary among spot beams in a hopping group. In some embodiments,the hopping plans consider the revisit time that the particularapplication needs. For example, voice over IP may need twenty to thirtymillisecond revisits to prevent a degradation in quality.

The hopping groups can be assigned to spot beams based on many differentstrategies. In one example, all the beams of a hopping group are next toeach other. For example, FIG. 16A shows a portion of the Field of Regardof FIG. 3, including 25 spot beams divided into five hopping groups offive spot beams each. Each of the hopping groups is shaded using adifferent type of shading. Hopping group 1 includes beams 3, 4, 5, 11and 12. Hopping group 2 includes beams 6, 7, 13, 14 and 15. Hoppinggroup 3 includes beams 20, 21, 29, 38 and 39. Hopping group 4 includesbeams 22, 30, 31, 40 and 41. Hopping group 5 includes beams 23, 24, 32,33 and 42. In some embodiments, the hopping plans between hopping groupswith spot beam members adjacent to spot beams members of other hoppinggroups are planned to avoid inter-beam interference

In other embodiments, each of the beams of a hopping group is uniformlyor non-uniformly distributed over the Field of Regard. For example, inthis embodiment, it is possible that each of the spot beams of a hoppinggroup utilize the same frequency range. The polarization can bedifferent between beams. FIG. 16B shows a portion of the Field of Regardof FIG. 3 including 25 spot beams divided into five hopping groups. Eachof the beams of a hopping group is shaded using the same type of shadingsuch that different shading is used for different hopping groups. Forexample, hopping group 1 includes beams 3, 14, 22, 32 and 38. Hoppinggroup 2 includes beams 4, 14, 21, 33 and 41. Hopping group 3 includesbeams 5, 11, 24, 33 and 39. Hopping group 4 includes beams 6, 15, 20, 30and 42. Hopping group 5 includes beams 7, 13, 23, 29 and 40.

In another embodiment, the hopping groups are arranged consecutivelyalong a path traversed by a subscriber terminal. For example, FIG. 16Cshows a portion of the Field of Regard of FIG. 3, with an arrowindicating the orbital direction. Each row of spot beams includes spotbeams in the same hopping group. In this embodiment, adjacent rows wouldhave different frequency ranges or different polarizations. In theembodiment of FIG. 16C, hopping group 1 includes spot beams 3, 4, 5, 6and 7. Hopping group 2 includes beams 11, 12, 13, 14 and 15. Hoppinggroup 3 includes beams 20, 21, 22, 23, and 24. Hopping group 4 includesbeams 29, 30, 31, 32 and 33. Hopping group 5 includes beams 38, 39, 40,41 and 42.

To graphically indicate time domain beam hopping, FIGS. 17A-17E depictfive different epochs in a hopping period for the embodiment of FIG.16B. In each of FIGS. 17A-E, the spot beam that is active for eachhopping group is shaded and the spot beams that are inactive for each ofthe hopping groups are not shaded. In the first epoch, depicted by FIG.17A, spot beams 4, 11, 22, 29 and 42 are active, while the other spotbeams are not active. In the second epoch, depicted in FIG. 17B, spotbeams 5, 12, 23, 50 and 41 are active, while the other spot beams areinactive. In the third epoch, depicted by FIG. 17C, spot beams 3, 14,20, 24, and 40 are active, while the other spot beams are inactive. Inthe fourth epoch, depicted by FIG. 17D, spot beams 7, 15, 21, 31, and 38are active, while the rest of the spot beams are inactive. In the fifthepoch, depicted in FIG. 17E, spot beams 6, 13, 32, 33, and 39 areactive, while the other spot beams are inactive. It is contemplated thatin some embodiments, a hopping period will have more than five epochs.However no specific number of epochs are required in a particularhopping period.

In some embodiments, the hopping period is completely configurable andprogrammable while the satellites are in orbit. This concept is depictedin FIG. 18 which shows a series of epochs divided into hopping periods.In this embodiment, each hopping period includes N epochs. After Nepochs, the next hopping period is performed. In some embodiments,consecutive hopping periods will perform the same hopping plan (e.g.,the same assignment of spot beams to epochs) until a satellite isprogrammed to change hopping plans (e.g., because demand has changed).During each hopping period, as depicted by FIG. 17A-17E, only one spotbeam of each hopping group is active. Therefore, only a portion of theField of Regard is active. Those spot beams that are active are referredto as the Field of View. As the number of active spot beams is less thanthe total number of spot beams in the beam map, each ofnon-geostationary satellites 302-322 has a Field of Regard that isgreater than its Field of View at any instance in time.

As discussed above, each of satellites 302-322 provide a plurality ofspot beams as the satellites move across the planet surface. In order toperform the time domain beam hopping, the spot beams are divided intohopping groups. The satellite uses the selection matrices describedabove, in conjunction with the digital channelizer, to perform the timedomain beam hopping. FIG. 19 is a flowchart describing one embodiment ofa process of a satellite performing the time domain beam hopping. Instep 670, the satellite reconfigures the selection matrices to routepower and make a connection to the applicable gateway beam to a next setof beams in the hopping groups according to the current hopping plan. Instep 672, the satellite will enable communication during epoch 0 (seeFIG. 18), only sending power and making gateway connection to thepredetermined subset of beams in each group. In step 674, the satellitewill reconfigure the selection matrices to route power to the next setof beams in the hopping groups according to the current hopping plan. Instep 676, the satellite will communicate during epoch 1, only sendingpower to a predetermined set of beams in each hopping group according tothe hopping plan. In step 678, the satellite will reconfigure theselection matrices to route power to the next set of spot beams in thehopping groups according to the current hopping plan. In step 680, thesatellite will enable communication during epoch 2, only sending powerto a predetermined subset of beams in each hopping group. This processwill continue for each epoch, as depicted in FIG. 18, until the lastepoch (designated as epoch N in FIG. 18). In step 682, the satellitewill reconfigure the selection matrix to route power to the next hoppinggroup beam sequence according to the current hopping plan. In step 684,the satellite will allow communication during epoch N, only sendingpower to a predetermined subset of beams in each hopping group. In step686, the satellite can (optionally) access a new hopping plan that takesinto account movement of the non-geostationary satellite. In step 688,the new hopping plan is loaded and becomes the current hopping plan,such that the process continues to step 670. Thus, the process of FIG.19 describes the operation of the non-geostationary satellite performingtime domain beam hopping during a hopping period. In one embodiment, thehopping plan can change at the end of each hopping period. In otherembodiments, the hopping plan can change after a fixed number or dynamicnumber of hopping periods. In other embodiments, the hopping period canchange after any hopping period; however, there is no requirement that ahopping plan change after any hopping period.

In one example embodiment, the hopping period is 90 seconds and an epochis 1.286334 milliseconds. In this embodiment, the time for a spot beamto drift completely across a subscriber terminal is approximately 2hopping periods (168 seconds).

In one example embodiment that uses time domain beam hopping for theuplink and downlink of the two hundred non-articulated spot beams, thetwo hundred non-articulated spot beams are divided into thirty sixhopping groups. Twenty-eight of the hopping groups include either six orseven spot beams that are not in the area at the Equator. Eight hoppinggroups include three or four spot beams that illuminate areas at theEquator. In one embodiment, the assignment of hopping groups is set andunchangeable in the satellites. In other embodiments, the membership ofthe hopping groups can be changed dynamically in orbit.

In one embodiment, the two hundred non-articulated spot beams aredivided into zones so that each hopping group can have one beam in eachzone (some hopping groups may have two beams in a zone). In one exampleembodiment, the non-Equatorial hopping groups will hop across six zonesarranged in a north/south grid. This leverages the tendency of eachcontinent's traffic to concentrate along a specific latitude. This alsodecreases the probability that a heavy demand is needed on one hoppinggroup in two locations and allows hopping groups to concentrate in anylarge geographic area of high traffic demand. For example, FIG. 20Ashows the same Field of Regard as FIG. 3 and indicates the Equator zone(rows 10, 11 and 12). The rest of the Field of Regard, other than theEquator zone, is the non-Equator region. Those spot beams in thenon-Equator region are shaded to indicate six zones. Each hopping groupwill include at least one beam in each zone. FIG. 20B shows the zonesfor the Equator zone. That is each of the spot beams in the Equator zoneis shaded one of four types of shading to indicate which one of the fourzones each spot beam is in. Each of the hopping groups for the Equatorzone will include no more than one beam in each zone. Thus the Equatorzone and the non-Equatorial region have separate zones for forminghopping groups. As such, the beam hopping is performed in the Equatorzone differently than the beam hopping in the non-Equatorial region. Inone embodiment, a different hopping plan is used for the Equator zonethan is used in the non-Equatorial region.

FIG. 21 is a table that shows one example of the 28 hopping groups usedfor the 170 non-articulated spot beams of the Field of Regard in FIGS.20A and 20B that are not in the Equator zone. The left hand columnindicates the hopping group number HG1-HG28. The other seven columnsindicates beam numbers for the beams in the relative hopping group. FIG.22 is a table describing membership of the hopping groups for theEquator zone. The left hand column indicates the hopping group numberEHG1-EHG8 and the other four columns indicate the beam numbers for thosebeams in the relative hopping groups.

FIG. 23 shows the Field of Regard of FIG. 3 (and FIGS. 20A and 20B) atone epoch. Each of the hopping groups depicted in FIGS. 21 and 22 hasone beam active at this particular epoch. Each of the active beams areshaded. Those active beams that are shaded represent the Field of Viewof the satellite at this epoch. While the entire beam represents theField of Regard. As can be seen, the Field of Regard for the satelliteis greater than the Field of View at this epoch.

FIG. 24 graphically depicts how the epochs are assigned to a set ofhopping beams in hopping group HG2 (see FIG. 21) over a portion of thehopping period. As can be seen, at no instance in time is any two beamsactive in the hopping group. That is only one beam is active at a time;however, the feeder beam which communicates with the gateway thatsupports beams 2, 24, 56, 79, 131, 154 and 190 is always active at eachepoch. That is, at each hop, one source beam and the feeder beam isactive for communication. The feeder beam is not part of the hoppinggroup but in some embodiments connectivity to the feeder beam can bechanged every hop. Thus, the gateways in the feeder beams are assignedtime epochs to manager their terminals within.

FIG. 25 depicts a super-frame which is the data format used during oneepoch. In one embodiment, the super-frame is based on the DVB-S2 xstandard. Other formats of super-frames or frames can also be used. Eachsuper-frame includes a usable portion 720 and an unusable portion.During the usable portion (or active time), data is transmitted. Duringthe unusable portion, no data should be transmitted. In one embodiment,the usable portion lasts for 1.2852 milliseconds. The unusable portionincludes a late arrival window 724, a payload transition time 722 and anearly arrival window 726. Late arrival window 724 lasts for 0.0665 μsand accounts for communication that is arriving at the satelliteslightly later than ought to be. Early arrival window 726 allows for0.0665 μs and accounts for any data for the next epoch that arrivesslightly early. Payload transition time 722 lasts for 1.001 μsec. Duringpayload transition time 722, the satellite is unavailable to communicatealong its various communication paths because the various selectionmatrices and/or the digital channelizer are adjusting/reconfiguring forthe next epoch. As can be seen the entire epoch lasts for 1.286334milliseconds. The technology described herein is not limited to anyspecific timing; therefore, other timing for the super-frame andtransmission can also be used.

An alternative embodiment includes adding beam hop transition timebetween super-frames. This could also be in terms of integer number ofsymbols to help clocks stay synchronized, if needed. This in effect addspadding time between defined super-frames in order to configuretransition time.

FIG. 26 also shows the same-super-frame of FIG. 25, but indicating thedata contents. The unusable portion of the super-frame, which includeslate arrival window 724, payload transition time 722 and early arrivalwindow 726, utilizes the time for transmitting 540 symbols. However, noreal data symbols will intentionally be transmitted during these timesby the satellite. The usable portion 720 of the super-frame includes aheader and a payload. The header, which uses 720 symbols, includes twofields: SOSF and SFFI. In one embodiment, SOSF is a start of asuper-frame preamble that is a unique combination of bits to indicate asuper-frame is starting. In one embodiment, SFFI is a super-frame formatindicator which indicates which of the different super-frame formatsthis particular super-frame is implementing. In one embodiment, morethan one super-frame format can be used for different types ofcommunication. In some embodiments, only one format will be used for thecommunication system. In one embodiment the payload is broken up into aset of capacity units (CU). In one embodiment, each CU is 90 symbols andrepresents a slot in the payload. In one example implementation, thecapacity units can be divided up between subscriber terminals within aspot beam so that different subscriber terminals will receivecommunication in different capacity units. This allows a type of timedomain multiplexing of the data path. As depicted in FIG. 27, oneembodiment of the Payload includes CU9-CU6800.

FIG. 28 describes some of the timing involved in the satellitecommunication system described herein. For example, FIG. 28 indicatesthat the propagation delay between the gateway and the satellite (SBpropagation delay) is approximately 54-72 msec. The processing delay ofcommunication through the satellite is approximately 20-30 μsec. Thepropagation delay from the satellite to the subscriber terminal for thenon-articulated spot beams performing time domain beam hopping (HBpropagation delay) is approximately 54 to 72 msec. Therefore, thesatellite will transmit to a subscriber terminal in a hopping beam datathat was sent by the gateway between 74 and 102 milliseconds previous.That is, the satellite is configured to receive data for a particularepoch that was sent previous to a start of the particular epoch by atime period that is significantly greater than the length of the epochitself. For example, the data for the particular epoch can be sent tothe satellite previous to the start of the particular epoch fortransmitting the data by a time period that is greater than 10 or 30times the length of the epoch. This requires very precise timing by thegateway.

There is a delay through the satellite payload so that the portion ofthe super-frame (see FIGS. 25 & 26) corresponding to payload transitiontime 722 enters the payload 20-30 μsec before it leaves the payload.Thus, the portion of the super-frame corresponding to payload transitiontime 722 is experienced/implemented by different portions of the payloadat different times. FIG. 6 shows one example of a payload that comprisesvarious selection matrices and a digital channelizer. Other switchingcomponents can also be used on the satellite. Different selectionmatrices and the digital channelizer may experience/implement payloadtransition time 722 at different moments in time. In one embodiment, thecomponents of the payload have to time their reconfigurations so thatthe payload transition time 722 arrives at the component when it needsto reconfigure. Thus, the payload transition time 722 is implemented bydifferent groups of switching components at different times such thatdifferent groups of switching components reconfigure for a new hoppingplan at different times.

FIG. 29 is a flowchart describing one embodiment of a process forperforming time domain beam hopping, as discussed above. In step 800,the system operates the constellation of non-geostationary satellitesalong the same orbital path using the same beam map. The beam map ofeach satellite is adjacent to a beam map on the adjacent satellite toprovide a composite beam map that circumnavigates the Earth. Eachsatellite provides a plurality of spot beams as the satellites movesacross the planet surface. In step 802, all or a subset of satellitesreceive in-orbit instructions that include one or more hopping plans orhopping patterns, as well as one or more user beam to gateway beamconnectivity plans. All gateways receive satellite dependent, timefrequency dependent allocations of one or more gateway beam's bandwidthaligned with provisioned satellite user beam and gateway beam hoppingpatterns. In step 804, based on the received instructions in step 802,one or more satellites reconfigure their user beam to gateway beamconnectivity (e.g., selection matrices and/or digital channelizer)and/or update their hopping plan based on the received new hoppingpattern (e.g., programming a non-geostationary satellite to assign anycombination of epochs in a hopping plan among spot beams of a samehopping group). In step 806, each satellite simultaneously performs timedomain beam hopping for the plurality of non-articulated spot beamsbased on the hopping group so that a subset of spot beams in eachhopping group are active at any given time. In one embodiment, each ofsteps 800-806 are performed continuously, and the process of FIG. 29 isperformed repeatedly. In one embodiment, each gateway performs TDMAconnectivity and sub-allocation according to its satellite-dependent,time-dependent, and user-beam-dependent gateway beam allocations. Thisgateway TDMA connectivity is implemented in independent timesynchronization with each of the one or more satellites to which it isprovisioned gateway beam allocations.

In one embodiment, the non-geostationary satellites described aboveincludes a forward path and a return path, such that the forward pathhas different hopping plans than the return path. That is, the beamhooping for the forward path can be different than the beam hopping forthe return. For example, the forward path can have different hoppinggroups, sequences and/or dwell times than the return.

Multiplexing Gateways

Looking back on FIG. 24, all the beams of a hopping group are switchedso that at any one given epoch one of the beams of the hopping group arein communication with a feeder beam. In another embodiment, the hoppinggroup can be in communication with multiple feeder beams that are timemultiplex. For example, FIG. 30 shows non-articulated spot beamsimplementing time domain beam hopping, including spot beams 2, 24, 56,79, 130, 154 and 190. At any given epoch, only one of those time domainbeam hopping spot beams will be active. FIG. 30 shows two feeder beamsFB1 and FB2. FB1 connects to one gateway. FB2 connects to a secondgateway. Thus, FIG. 30 shows a first plurality of spot beams (2, 24, 56,79, 130, 154 and 190) and a second plurality of spot beams (FB1 andFB2). At any epoch, one spot beam of the hopping beams is active and onespot beam of the feeder beams is active in order for the two activebeams to communicate. Thus, each of satellites 302-322 are configured toprovide a first plurality of spot beams (e.g., spot beams 24, 56, 79,130, 154, 190) for communication with subscriber terminals using timedomain beam hopping to move throughput between spot beams of the firstplurality of spot beams and a second plurality of spot beams (e.g., FB1and FB2) adapted for communication with gateways. The satellites eachinclude a spectrum routing network (one or more of the selectionmatrices and/or channelizer) that is configured to time multiplex thespot beams of the second plurality of spot beams with spot beams of thefirst plurality of spot beams. That is, each active time hopping beamcan communicate with either one of the feeder beams at different epochs.For example, spot beam 130 communicates with FB2 at epoch E4 and FB1 atepochs E5 and E6, all while spot beam 130 remains over a subscriberterminal location on the planet surface. Similarly, spot beam 2communicates with FB1 and epochs E0, E1, E2 and E3 and communicates withFB2 at epochs E7 and E8, all while spot beam 2 remains over a subscriberterminal location on the planet surface. In one embodiment, a spotbeam's communication with a first gateway can be interleaved with itscommunication with a second gateway so that the respective sets ofepochs are interleaved (set of epochs 18, 19 and 23 intermixed with setof epochs 20, 21, 22 and 24). When more than one gateway is supported ina feeder beam the N gateways may operate on different frequencies or thesame frequency. If operating on one frequency each gateway will have adifferent epoch assigned for transmission and reception.

FIG. 31 is a flowchart describing one embodiment of a process forperforming time domain beam hopping with time multiplexing gateways, asdepicted in FIG. 30. The process of FIG. 31 is continuously performed byeach of satellites 302-322. In step 840, each satellite provides a firstplurality of spot beams in order to communicate with subscriberterminals, as the satellites move across the planet surface. In step842, the satellites will perform time domain beam hopping for the firstplurality of spot beams. In step 844, each of the satellites provides asecond plurality of spot beams in order to communicate with thegateways, as the satellites move across the planet surface. In step 846,each satellite provides time multiplexing of the spot beams of thesecond plurality of the spot beams with the spot beams of the firstplurality of spot beams while a particular spot beam of the first set ofspot beams remains over a particular location (e.g., routecommunications between different beams of the second plurality of spotbeams and a particular beam of the first plurality of spot beams atdifferent epochs of multiple epochs during the hopping period).

FIG. 31 shows one example implementation of step 846 includes steps 846Aand 846B. In step 846A, a satellite provides communication between aparticular spot beam of the first plurality of spot beams and a firstspot beam of the second plurality of spot beams during a first set ofepochs while the particular spot beam is over a location on the planetsurface (e.g., while illuminating a set of one or more subscriberterminals). In step 846B, the satellite provides communication betweenthe particular spot beam and a second spot beam of the second pluralityof spot beams during a second set of one or more epochs while theparticular spot beam remains over the location on the planet surface. Soduring a particular hopping period, a hopping beam can communicate withdifferent feeder beams.

FIG. 32 provides a flowchart describing one embodiment of a process forperforming time domain beam hopping on a satellite that includes themultiplexing of gateways as described above. In step 860, the satellitetransmits data for the current epoch for the current set of servicebeams and feeder beams, as routed by the channelizer and the variousselection matrices. In step 862, the satellite transmits data thatarrived late for the current epoch for the current set of service beamsand feeder beams as routed by the channelizer and selection matrices. Inone embodiment, step 860 corresponds to transmitting the payload of asuper-frame and step 862 corresponds to transmitting the late arrivalwindow 724 of a super-frame (see FIG. 26). In step 864 of FIG. 32,satellite reconfigures routing of all or some (or none) of the routingpaths of the channelizer and selection matrices to set up communicationfor service beams with different one or more feeder beams, andreconfigures the selection matrices for the next hopping arrival. In oneembodiment, step 864 corresponds to reconfiguration time 722. In step866, the satellite transmits data that arrives early for the next epochfor the new set of service beams and feeder beams as routed by thechannelizer and selection matrices. In one embodiment, step 866corresponds to early arrival window 726. Step 860-866 correspond to oneepoch. If this epoch was not at the end of a hopping period (step 868),then the process will continue back at step 860 to perform transmissionof data for the next epoch. However, if this epoch was the last epoch ofthe hopping period (step 868), then the satellite can load a new hoppingplan and new gateway multiplexing plan. In one embodiment, step 870 isoptional. After step 870, the process loops back to step 860 andperforms the next epoch for the next hopping period.

Allocating Throughput

As discussed above, the hopping plan assigns different epochs todifferent beams of the hopping group. Thus, the system can allocatedifferent amounts of throughput to each beam of the hopping group, wherethe amount of throughput allocated corresponds to the number of epochsassigned to the particular beam of the hopping group. In one embodiment,the amount of throughput (the amount of epochs) assigned to each hoppingbeam is based on demand of users within the coverage area during a givenhopping period. In some embodiments, as discussed above, thenon-articulated spot beams can be used to service both subscriberterminals and gateways. In that situation, the allocation of throughputto a spot beam can be based on the throughput needs of the gateway inthe spot beam as well as the subscriber terminals in the spot beams.Thus, the number of epochs assigned to that spot beam is based on theneeds of the gateway and the needs of all the subscriber terminals. Notethat the epochs assigned to a beam for a hopping plan can be continuousor non-continuous (spaced apart in time).

FIG. 34 depicts an embodiment where a satellite is configured to providea plurality of spot beams adapted for communication using time domainbeam hopping to switch throughput among spot beams of a hopping group,where the plurality of spot beams includes at least one spot beam thatilluminates and communicates with a gateway and a plurality ofsubscriber terminals. A satellite is configured to implement a beamhopping plan that during a hopping period provides throughput to thefirst spot beam for an aggregated time duration (e.g., number of epochs)based on the bandwidth assignments to the gateway and the plurality ofsubscriber terminals. Note that the performing time domain beamedhopping for the spot beam includes providing throughput to the spot beamfor a non-continuous set of multiple epochs that form the aggregatedtime duration. For example, FIG. 33 shows satellite 201 providing spotbeams 950, 952 and 954 in hopping group A and spot beams 956, 958, and960 in hopping group B. Satellite 201 also provides steerable feederbeam 962. Non-articulated spot beam 950, at this point in time,illuminates and communicates with subscriber terminals ST and a gatewayGW. Spot beam 952 also communicates with subscriber terminals ST and agateway GW. Spot beam 954 communicates only with subscriber terminalsST. Spot beams 956, 958 and 960 only communicate with subscriberterminals ST. Because spot beams 950, 952 and 954 are in a same hoppinggroup, satellite 201 performs time domain beam hopping such that onlyone of those three spot beams are active at a given time. That meansthat only one of gateway 950 and 952 can be active at the same time.Thus, the performing time domain beam hopping for the plurality of spotbeams includes providing throughput to multiple gateways over time thatare geographically separated from each other because they are inseparate spot beams. In the embodiment depicted in FIG. 33, the amountof throughput provided to spot beam 950 (e.g., number of epochsassigned) is based on the throughput needs of the subscriber terminalsas well as the throughput needs of the gateway in spot beam 950. Theamount of throughput provided to spot beam 952 (e.g., the number ofepochs assigned in the hopping plan) includes enough throughput (e.g.,epochs) to service the subscriber terminals ST in spot beam 952 as wellas servicing the gateway GW in spot beam 952. Note that spot beam 954does not include a gateway. In one embodiment, each of the subscriberterminals in spot beam 954 can communicate with either the gateway inspot beam 950 or the gateway in spot beam 952 by multiplexing betweenthe two gateways, as described above.

FIG. 34 is a flowchart describing one embodiment of a process foroperating a satellite that includes performing time domain beam hoppingfor the plurality of spot beams including implementing a beam hoppingplan that during a hopping period provides throughput to first spot beamfor an aggregated time duration based on bandwidth assignments of thegateway and subscriber terminals in that spot beam. In step 902, thesystem will determine demand over time for the subscriber terminals.This can be performed at the network control center. In step 904, basedon the beam map, gateways are assigned to various hopping groups. Instep 906, the system determines the bandwidth needs of the service links(communication with subscriber terminals) based on the demand over timeof the subscriber terminals. In step 908, the bandwidth needs of thefeeder links (communication with gateways) in the hopping beams will bedetermined based on demand of the subscriber terminals in communicationwith the gateways. In step 910, bandwidth will be determined for thefeeder links in dedicated feeder beams (e.g., the steerable beams asopposed to the non-articulated beams that are shared between subscriberterminals and gateways). In step 912, a hopping beam plan will becreated for the multiple/different hopping periods. In step 914, thecreated hopping plans are transmitted to all the satellites while thesatellites are in orbit. For example, the network control center willtransmit the hopping plans to the satellite when the satellites passover or by the network control center. These hopping plans are receivedby the satellites and stored in the memory for the satellites. In step916, each satellite will update or otherwise change its current hoppingplan so that a new hopping plan is implemented at the appropriate timeor times. The satellites each perform time domain beam hopping of theplurality of non-articulated spot beams including implementing athen-current beam hopping plan that during a hopping period providesthroughput to one or more spot beams for an aggregated time durationbased on the bandwidth assignments of gateways and subscriber terminals.

FIG. 35 is a chart describing one example of sharing capacity bydividing up epochs or CUs in the epoch based on pro rata throughputneeds. For example, FIG. 35 shows the dividing up of CUs or epochs forhopping group A, hopping group B and beam 962 of FIG. 33. As beam 962only includes a single gateway, all time is available to that gateway.In some embodiments, there can be multiple gateways in spot beam 962 sothat the throughput of spot beam 962 must be divided among the multiplegateways. Hopping group B includes three beams that only includessubscriber terminals. The amount of throughput (or epochs) provided tobeam 956 is represented in FIG. 35 as 956S. The amount of throughputprovided to beam 958 is represented as 958S. The amount of throughputprovided to spot beam 960 is represented as 960S in FIG. 35. As can beseen, the amount of throughput or number of epochs is not dividedequally among the three spot beams. In FIG. 35, the amount of throughputor epochs provided to spot beam 954 (that does not include a gateway) isrepresented by box 954S. The amount of throughput or epochs provided tospot beam 950 is represented by two components: one component 950Saccounting for the throughput assignment to subscriber terminals and asecond component 950G representing the assignment of throughput to thegateway in spot beam 950. Since, in beam 950, the gateway may usedifferent frequency than the users the first and second component canexist simultaneously. The amount of throughput or epochs provided tospot beam 952 includes two components: 952S represents the amount ofthroughput assignment accounted for the subscriber terminals and 952Grepresents the assignment of bandwidth for gateway. Since, in beam 952,the gateway may use different frequency than the users the first andsecond component can exist simultaneously.

As mentioned above, in some embodiments there can be multiple gatewaysin a gateway beam. These multiple gateways can support (ie communicatewith) different subscriber terminal sets in the same one or more spotbeams that perform time domain beam hopping or support (ie communicatewith) different subscriber terminal sets in the different one or morespot beams that perform time domain beam hopping. In anotheralternative, these multiple gateways can support (ie communicate with)the same subscriber terminals. The multiple gateways in the same spotbeam will use different epochs to communicate with the subscriberterminals.

In some embodiments, a satellite has two or multiple spot beams in ahopping group that illuminate and communicate with gateways andsubscriber terminals, where the gateways are geographically separatedfrom each other. For the multiple spot beams that illuminate andcommunicate with gateways and subscriber terminals, they are allindividually assigned frequency throughput for a total time durationbased on throughput assignments of the respective gateways andsubscriber terminals. Therefore, the satellite performs time domain beamhopping, including providing throughput to multiple gateways over timethat are geographically separated from each other.

In regard to the constellation of satellites 302-322, the providing aplurality of spot beams and performing time domain beam hopping for theplurality of spot beams are performed separately and concurrently bymultiple satellites using a same beam map and traveling along a sameorbital path.

In one embodiment, the satellite is configured to switch throughput at anumber of epochs based on the uplink and downlink demand from userterminals in the hopping group beam members. In another embodiment, thesatellite is configured to switch throughput at a number of epochs basedon the uplink and downlink demand from user terminals and gateways inthe hopping group beam members.

Beam to Beam Handover

As each of satellites 302-322 move in orbit, their Fields of Regardmove, causing each of the spot beams' coverage areas to move. As asubscriber terminal reaches the edge of a spot beam it must be handedover to the next spot beam on the same satellite. Typically, thehandover will be from a spot beam in a first hopping group to a spotbeam in a different hopping group. This may cause the updating ofhopping plans to account for the subscriber terminal(s) changing hoppinggroups. When the subscriber terminal reaches the edge of a spot beam atthe edge of the Field of Regard, then the subscriber terminal is handedover to the next satellite.

FIG. 36 graphically depicts a portion of the satellite communicationsystem, showing a handover of subscriber terminal between spot beams ofthe same satellite. For example, FIG. 36 shows satellite 201 travelingin the orbital direction 201A providing spot beam 980 and spot beam 982.As satellite 201 moves in direction 201A, subscriber terminal ST willmove from spot beam 980 to spot beam 982; therefore, a handoff mustoccur. FIG. 36 shows spot beam 201 in communication with gateway 984(which includes antenna 986). In one embodiment, gateway 984 includesmodem 990 connected to antenna 986, network interface 994 connected tonetwork 988 (which may be the Internet or other network), and gatewayprocessor 992 which is connected to modem 990 and network interface 994.In one embodiment, gateway processor 992 can be a computing device thatincludes one or more microprocessors, memory, nonvolatile storage, etc.

Because subscriber terminal ST is being handed over from spot beam 980to spot beam 982, gateway processor 992, which receives messages fromnetwork 988 to be sent to subscribe terminal ST, must communicate thosemessages via the appropriate spot beam. For example, FIG. 36 showsgateway 984 communicating messages A, B, C and D. Because the timing ofthe transmission of the messages (in light of the hopping plan), messageA and message B will be transmitted from the satellite 201 to subscribeterminal ST while subscriber ST is in spot beam 980. Messages C andmessage D will be transmitted from satellite 901 to subscribe terminalST while subscribe terminal ST is in spot beam 982. Note that spot beam980 and 982 are among the non-articulated spot beams that implement timedomain beam hopping. Furthermore, spot beam 980 has a differentfrequency range than spot beam 982, but both spot beams use the samepolarization. In other hopping arrangements, spot beams 980 and 982 canhave the same frequency range or overlapping frequency ranges.

FIG. 37 is a flow chart describing one embodiment of a process performedby the gateway for performing handover of subscriber terminal betweenspot beams on the same satellite. In step 1002, gateway processor 992determines new handover times for all terminals connected to thatparticular gateway based on the satellite's location, the known beampattern and the known beam hopping plan(s) as well as the position ofthe terminals (or feedback of the signal strength received by thesubscriber terminals from the satellite). In step 1004, gatewayprocessor 992 determines (calculates or looks up in a database) newhopping plan(s) for the spot beams based on updated terminals and thebeams. For example, when subscriber terminal ST transitions from beam980 to beam 982 that may affect the hopping plan due to a change indemand. In step 1006, gateway 984 will broadcast the handoverinformation to all the terminals in all the spot beams communicatingwith the gateway 984. The handover information includes a set ofrecords, with each record including a terminal ID for the subscriberterminal, old spot beam, new spot beam, and time of handover. Otherinformation could also be provided. In step 1008, the gateway broadcastthe new hopping plan to the terminals and the satellite. In oneembodiment, the satellite already has the hopping plan and does not haveit communicated from the gateway.

FIG. 38 is a flow chart describing one embodiment of a process performedby the gateway for performing a handover of the subscriber terminal, atthe time of hand off. In step 1040, gateway processor 992 receives datafrom network 988, which is to be transmitted to subscriber terminal ST.In step 1042, gateway processor 992 determines the time for transmissionof that received data from the satellite 201 to subscriber terminal ST.In step 1044, gateway processor 992 checks the latest handoverinformation (see step 1006 in FIG. 37). In step 1046, gateway processor992 determines whether the time that the satellite will be transmittingthe data to the subscriber terminal is near handover time. If that timeis not near the handover time, then in step 1048 gateway processor 992communicates the received data using the current hopping plan and thecurrent hopping group as well as normal margins for Adaptive Coding andModulation (ACM) and Time Domain Beam Hopping (TDM). In one embodiment,the margins for TDM relate to the size or timing of the late arrivalwindow and early arrival window. If the time for transmission form thesatellite is near the handover time but before the handover time, thenstep 1050 gateway processor 992 communicates the data to the terminalusing the pre-handover hopping beam, of the pre-handover hopping groupand wider margins (if needed) for ACM and TDM. If the time fortransmission from the satellite to the terminal is to be after thehandover time, then gateway processor 992 communicates the data usingthe post-handover hopping beam of the post-handover hopping group andwider margins (if needed) for ACM and TDM.

FIG. 39 is a flow chart describing one embodiment of a processorperformed by a subscriber terminal in regarding to handing over thesubscriber terminal between spot beams. The process FIG. 39 is performedin response to the gateway performing the processor FIG. 37. In step1060 FIG. 39, the terminal receives broadcasted handover information(see step 1006 of FIG. 37). In step 1062, if the received broadcastincludes handover information for that terminal, then that terminalstores the information and will configure it during an epoch when thebeam is not active or during the payload transition time. Note that theprocesses of FIGS. 37 and 39 are performed continuously.

FIG. 40 is a flow chart describing one embodiment performed by asubscriber terminal at the time for a handover between spot beams. Itwas noted that in step 1062, an interrupt is configured. That interruptwill trigger the performance of the process of FIG. 40. In step 1070, itis determined whether the terminal is at or near a time of a handover.If not, and the terminal receives data in step 1072 (in response to step1048 of FIG. 38), then the terminal decodes that data in step 1074 usingnormal margins for ACM and TDM. The data is reported to a client in step1076. A client for a subscriber terminal can be a computing device,smart appliance, etc. If, in step 1070, is determined that the terminalis near a handover time, but before the handover time, then in step1080, the terminal will receive data from the satellite and decode thatdata in step 1082 using the wider margins for ACM and TDM. The data willthen be reported in step 1076. If the terminal is at a time for handoverthen in step 1086 the terminal retunes its local oscillator to changefrequencies to the master frequency for the new spot beam. That is,looking back at FIG. 36, subscriber terminal ST will retune its localoscillator from the frequency for spot beam 980 to the frequency forspot beam 982. In step 1088, the hopping plan will be updated. In someembodiments, the terminal keeps tracking of the hopping plan. In otherembodiments, the terminal will not keep track of the hopping plan. Inone embodiment, a subscriber terminal will include one antenna and oneoscillator. In other embodiments, the subscriber terminal includes twoantennas and two oscillators to alternate using terminals andoscillators between spot beams.

FIG. 41 depicts a portion of a satellite communication system showing ahandover of a subscriber terminal between spot beams of differentsatellites. For example, FIG. 41 shows satellite 1100 and satellite1102, which can be any pair adjacent satellites of satellite 302-322.Satellite 1102 provides spot beam 1106. Satellite 1100 provides spotbeam 1104. The subscriber terminal 1108 includes two antennas 1110 and1112, two modems 1114 in communication with antenna 1110 and modem 1116in communication with antenna 1112, terminal processor 1116 and networkinterface 1118 which is connected to a local area network (LAN).Terminal processor 1116 can be any computing device suitable thatincludes a processor, memory, nonvolatile memory and appropriatecommunication interfaces.

In FIG. 41, subscriber terminal 1108 is positioned in a region thatrepresents where spot beam 1106 overlaps with spot beam 1104. Gateway1120 is communication with both satellites 1100 and 1102. Gateway 1120includes a first antenna 1124 for communicating with satellite 1100.Gateway 1120 includes antenna 1122 for communicating with satellite1102. Gateway 1120 includes a first modem 1128 connected to antenna 1124to second modem 1126 connected to antenna 1122. Gateway 1128 includesgateway processor 1130 connected to both modem 1126 and 1128. Gatewayprocessor 1130 is also connected to network interface 1132, which cancommunicate with the Internet or other network. Because gateway 1120 isin communication with both satellites, and utilizes one processor 1130,when the subscriber terminal hands over from satellite 1102 to satellite1100 the communication between subscriber terminal 1108 and gateway 1128will not be broken. So as satellites 1102 and 1100 move west to east,causing subscriber terminal 1108 to transition from spot beam 1106 onsatellite 1102 to spot beam 1104 on satellite 1100, the communicationpath between subscriber terminal 1108 and gateway 1128 will change fromgoing via satellite 1102 to going via satellite 1100. Gateway 1120 willperform the process of FIG. 37 described above for identifying andcommunicating the handover information.

Additionally, gateway will perform the process depicted in FIG. 42 forhanding over a subscriber terminal between spot beams of differentsatellites. In step 1200, gateway processor 1130 communicates with thecurrent satellite via first antenna (e.g., antenna 1122). In step 1202,gateway 1120 establishes communication with the new satellite via asecond antenna 1124. In step 1204, the gateway determines when theswitch terminals to the new satellite based on the handover informationdescribed above. Gateway 1120 will inform the satellites and thesubscriber terminals as per the process of FIG. 37. In anotherembodiment, the satellites are preprogrammed as to when to switch. Inanother embodiment, the gateway informs the network control center. Instep 1206, the gateway communicates with the terminal via the currentsatellite (e.g., satellite 1102) until the handover time, performing theprocess of FIG. 38 using the first antenna (antenna 1122) and thecurrent beam hopping plan. In step 1208, the gateway communicates withthe terminal via the new satellite (satellite 1100) after the handovertime using the new hopping plan, performing the process of FIG. 30 usingthe second antenna (e.g., antenna 1124). The subscriber terminal willperform the process of FIG. 39, as described above, to receive the newhandover information. Additionally, the subscriber terminals willperform the process of FIG. 43 at the time of handover. In step 1250,the gateway decides whether the subscriber terminal is at or near thesatellite handover time. If the subscriber terminal is not at or near asatellite handover time, then step 1252, data will be communicated withthe satellite via its first antenna (e.g., antenna 1110). In step 1254,the gateway will decode received data using normal margins for ACM andTDM. In step 1256, received data will be reported to the client. Notethat data that is transmitted will not need to be decoded and reported,but rather would be encoded.

If, in step 1250, it is determine that the subscriber terminal is nearhandover time, then at step 1260, the terminal will establish ormaintain a connection with the gateway via the second antenna and secondsatellite. In step 1262, the subscriber terminal will continuecommunicating data with the satellite via the first antenna. In step1264, received data will be decoded by the gateway using wider marginsfor ACM and TDM. In step 1266, data received will be reported. Data thatis being transmitted will be encoded using wider margins for ACM andTDM, if ACM is being used on the up link for the return path.

If in step 1250, it is determined that the subscriber terminal is at thehandover time, then step 1270, the subscriber terminal switch tocommunicating data with the second or new satellite via the secondantenna. In step 1272, a new hopping plan will be implemented. In oneembodiment, the subscriber terminal does not know what the hopping planis and just reacts to data from the gateway and, therefore, will not beaware of the new hopping plan. In step 1274, data received will bedecoded using wider margin for ACM and TDM. Data transmitted will usewider margins for ACM, if ACM is being used. Data received will bereported in step 1276.

The above description of beam to beam handovers includes communicating,at a ground base terminal, with a non-geostationary satelliteconstellation using a first spot beam of the non-geostationary satelliteconstellation and the first beam hopping plan; and the ground basedterminal changing the communicating with the non-geostationary satelliteconstellation to use a second spot beam of the non-geostationarysatellite constellation in a second hopping beam.

Handover for Multiple Gateways

As described above, some of the non-articulated spot beams 1-200 foreach of the satellites 302-322 can be used to service subscriberterminals and gateways. In some embodiments, subscriber terminals in thenon-articulated spot beams are configured to communicate with gatewaysin the non-articulated spot beams. In such embodiments, the group ofsubscriber terminals communicating with the gateway and thenon-articulated beams will need to communicate with at least twogateways. In one implementation, the two gateways communicating with thegroup of subscriber terminals are in the same country as the subscriberterminals in order to comply with local laws restricting communicatingacross borders. In other embodiments, the two gateways can be indifferent countries.

FIG. 44 shows an example configuration where two gateways 986 and 988communicate and service subscriber terminal ST via Satellite 1. Each ofthe gateways has its own antenna and its own modem. For example, gateway986 includes modem 991 and gateway 988 includes modem 993. Neithergateway includes a gateway processor. Rather, both modems 991 and 993communicate with a central processor 992 which is in communication withthe network interface 984 for communicating on network 988 (e.g.,Internet). By sharing a central processor 992, streams of communicationbetween the subscriber terminal ST and entities on network 988 may bemaintained in a manner with no apparent interruption. In one embodiment,gateway 986 is located at the western edge of the subscriber terminalsand gateway 988 is located at the eastern edge of the subscriberterminals. Therefore, these gateways can be referred to as the easterngateway and the western gateway. The reason for locating the gateways onthe western edge and the eastern edge is because the satellites 302-322move from west to east and locating the gateways at the western edge andthe eastern edge (separated in the orbital direction) allows forefficient handovers. In other embodiments where the satellites travel ata different orbital direction, the gateways will be located at differentlocations that are separated from each other by different orbitaldirections. That is, the first gateway will be a first location, thesecond gateway is at a second location, and the second location isseparated from the first location in the orbital direction.

FIG. 45 is a flow chart describing one embodiment of a process forperforming the handover between satellites, with the use of eastern andwestern gateways, where the gateways are operating within andcommunicating with spot beams implementing time domain beam hopping.Note that rather than using eastern and western gateways, the sameprocess can be used for two different gateways at two differentlocations separated in the orbital direction. In step 1350, all or asubset of subscriber terminals communicate with the eastern gateway viasatellite 1 as the non-articulated spot beam implementing time domainbeam hopping traverse the region where the subscriber terminals arelocated. FIG. 46A shows the time when step 1350 is performed. Field ofRegard for satellite 1 is completely covering spot beams A, B, C, D, J,F, and G, which are the spot beams for which the subscriber terminalsare located. At the eastern edge of spot beam C is eastern gateway E.The western edge of spot beam J is western gateway W.

In step 1354, western gateway W hands over to satellite 2, as soon aspossible (or as close to as soon as possible). For example, FIG. 46Bshows that the Field of Regard for Satellite 2 is very close to spotbeam J, close enough to allow western gateway W to connect to Satellite2.

In step 1356, as the Field of Regard for Satellite 2 passes over thespot beams, subscriber terminals in the spot beams under the Field ofRegard for Satellite 2 begin to connect to Satellite 2. As discussedabove, the subscriber terminals will be told ahead of time of thehandover information. Thus, when subscriber terminals handover toSatellite 2, they will begin to connect to and communicate with thewestern gateway via Satellite 2. For example, FIG. 46J shows a portionof the Field of Regard for Satellite 2 over spot beams A, J and G, andthe Field of Regard for Satellite 1 over spot beams A, G, D, B, C and F.Subscriber terminals in spot beams A, J and G will have connected toSatellite 2 and began communicating with gateway W via Satellite 2.

After all the terminals in spot beams A, B, C, D, J, F, and G havehanded over to Satellite 2 and are in communicating with westerngateway, the eastern gateway E will handover to Satellite 2. Forexample, FIG. 46D shows all five spot beams within the Field of Regardfor Satellite 2; therefore, all the subscriber terminals have beenhanded over and connected to Satellite 2 and are in communication withthe western gateway via Satellite 2. In step 1360, in response ofinstructions from the central processor 992, all of the subscriberterminals will then switch to communicating with the eastern gateway Evia Satellite 2. The process of FIG. 45 will then be performed againwith Satellite 3 (not depicted), then with satellite 4 (not depicted),etc. In this manner, the plurality of subscriber terminals areconfigurable to communicate with central processor 992 via thenon-geostationary satellites via the first eastern gateway or thewestern gateway. The central processor 992 is configured to assign eachsubscriber terminal to communicate with the central processor 992 viathe eastern gateway or the western gateway based on location of theappropriate non-geostationary satellite.

In some embodiments, the eastern gateway (and some subscriber terminals)and the western gateway (and some subscriber terminals) are in differentnon-articulated spot beams that implement time domain beam hopping andthat are in the same or different hopping groups performing the same ordifferent hopping plans.

Steerable Gateway Beams

As discussed above with respect to FIG. 2, each of the satellites302-322 include eight steerable 4.2 degree gateway beams and sixsteerable 2.8 degree gateway/high capacity subscriber terminal beams.Additionally, each of the non-geostationary satellites of theconstellations configured to provide a first plurality of two hundrednon-articulated spot beams that comprise the Field of Regard. Thesteerable spot beams can be steered to establish communication with agateway outside of and in front of the Field of Regard and maintain thatcommunication while the satellite and the Field of Regard move over andthe past the gateway including when the gateways outside of and behindthe Field of Regard for the respective satellite. This enables thegateways to establish connection with the satellite prior to the spotbeams covering the subscriber terminals and then maintain connection tothe satellite while the subscriber terminals handover to the satelliteand while the subscriber terminals handover to the next satellite toallow seamless communication for the subscriber terminals. Thisconfiguration is depicted graphically in FIG. 47 which shows satellite1400 and satellite 1402. Satellite 1400 provides non-articulated spotbeam 404 which implements time domain beam hopping for communicatingwith the plurality of the subscriber terminals ST. Satellite 1402provides non-articulated spot beam 1406 that implements time domain beamhopping for communication with a plurality of subscriber terminals ST.It is possible that both satellites 1400 and 1402 are simultaneously incommunication with gateway 1120. In another embodiment, epochallocations are made to non-articulated beams such that no beam hoppingis required in a geographic area.

In one embodiment, gateway 1120 includes two antennas, including antenna1122 for communicating with satellite 1402 (the eastern satellite) andantenna 1124 for communicating with satellite 1400 (the westernsatellite). As the satellites of the constellation move west to east,the gateway's antennas will be in communication with different pairs ofsatellites. Gateway 1120 includes the modem 1126 in communication withantenna 122 and modem 1128 in communication with antenna 1124. Gateway1120 also includes gateway processor 1130 that is in communication withmodem 1126, modem 1128 and network interface 1132 (which connects to theInternet or other network). The spot beams that satellite 1402 and 1400use to connect to gateway 1120 are steerable so that they can remainpointed at the gateway as the satellites and the Field of Regards move.This is described in more detail with respect to the flow chart of FIG.48 and the graphs of FIGS. 49A-E.

In step 1430 of FIG. 48, the gateway is connected to satellite 1 viasteerable spot beam for satellite 1 in order to communicate with itssubscriber terminals via satellite 1. In step 1432, while the gateway iscommunicating with subscriber terminals via satellite 1 (e.g., thegateway is in the Field of Regard satellite 1) and the gateway is not inthe Field of Regard of satellite 2 because the gateway is east (infront) of satellite 2, the gateway establishes synchronization withsatellite 2 using the timing beacon for satellite 2 (timingsynchronization aligns gateway forward burst with the allocated timeslot reference on the satellite). In step 1434, satellite 2 moves itssteerable beams (e.g., beams 286, 288, 290, 292, 294, 296, 270, 272,274, 276, 278, 280, 282 or 284 of FIG. 2) to point at the gateway andthe gateway initiates a forward link for communication with thesubscriber terminals. FIG. 49A depicts the situation existing at thetime of step 1434.

FIG. 49A shows the gateway GW surrounded by five coverage areas B1, B2,B3, B4 and B5 each of those coverage areas B1-B1 include a plurality ofsubscriber terminals that are supported by and are in communication withthe gateway. FIG. 49A shows that the Field of Regard for satellite 2 iseast of the gateway and the coverage areas B1-B5 such that is notcovering or overlapping with the gateway or the coverage area of B1-B5.Despite the fact that the gateway is outside the Field of Regard forsatellite 2, satellite 2 points/moves one of its steerable beams tocover (point at) and communicate with the gateway.

In step 1436, satellite 2 establishes internal connectivity to servicethe gateway, including providing initial bandwidth to the steerable spotbeam for establishing communication. Satellite 2 provides connectivityfor the gateway to communicate via the steerable spot beam withsubscriber terminals. In step 1438, as the non-articulated spot beamsperforming time domain beam hopping (and the Field of Regard) traverseacross the coverage region supported by the gateway, additionalterminals handover to satellite 2 and re-establish communication withthe gateway. For example, FIG. 49B shows a portion of the Field ofRegard for satellite 2 covering and including coverage areas B1 and B5.Therefore, subscriber terminals in coverage areas B1 and B5 will havehanded over to satellite 2 and established communication with gateway GWvia satellite 2.

As discussed above, the steerable beams can include a single purposebeam that only communicate with gateways or dual purpose beams that cancommunicate with gateways and subscriber terminals. If the steerablespot beam that is pointed to and communicating with the gateway is adual purpose spot beam, then as that dual purpose spot beam traversesacross the Field of Regard, including the non-articulated spot beamsimplementing time domain beam hopping, the system can optionally use thesteerable spot beam for communicating with the subscriber terminals. Ifthe system uses the steerable spot beam to communicate with thesubscriber terminals, then the non-articulated spot beams that implementtime domain beam hopping that overlap with the steerable spot beam will(optionally) be turned off while they overlap with the steerable spotbeam. When these non-articulated spot beams are turned off the one ormore epochs that they would have been assigned in the hopping plan arethen provided to other spot beams in the same hopping group in step 1440In step 1442, as more subscriber terminals establish communication withthe gateway (due to movement of satellite 2), satellite 2 provisionsmore bandwidth to the gateway including updating internal connectivityto provide additional bandwidth. That is, the steerable spot beam can beable to communicate using multiple colors (see frequency plan describedabove). Initially one color can be provided to the spot beam. As moresubscriber terminals connect to the gateway, additional colors can beadded to the non-articulated spot beams frequency allocation. FIG. 49Cshows the Field of Regard for satellite 2 encompassing the gateway incoverage regions B1-B5. Therefore, all the subscriber terminals that aresupported by gateway GW are now communicating with gateway GW viasatellite 2. As satellite 2 moves from its position in FIG. 49A to itsposition in FIG. 49C, it adjusts the pointing of the steerable spotbeams so that the steerable keeps pointing at gateway GW. In step 144,the gateway breaks its connection with satellite 1 as satellite 1 ismoved to orbital position in which it can no longer service anysubscriber terminals supported by the gateway, thus freeing up thesteerable spot beam that satellite 1 was using to point at the gatewayto be used for another gateway.

In step 1446, as the Field of Regard for satellite 2 leaves the regionsupported by the gateway, additional subscriber terminals start tohandover to satellite 3 for communication with the gateway via satellite3. Not that in between steps 1444 and 1446 is an arrow 1445. That arrowindicates when the process of FIG. 48 is started again for satellites 2and 3 (rather than satellites 1 and 2). In step 1448, as most subscriberterminals stop communication with the gateway via satellite 2, satellite2 provisions less bandwidth to the gateway, including configuringinternal connectivity (the selection matrices and digital channelizer)to reduce the provisioned bandwidth for the steerable spot beam pointingat gateway GW. FIG. 49D shows the Field of Regard of satellite 2 movingeast of gateway GW and only covering coverage areas B2 and B3, as wellas a small portion of coverage area B4. At this point, subscriberterminals in coverage areas B1 and B5 have handed over to the nextsatellite. The gateway remains in contact with satellite 2 as long assatellite 2 is in an orbital position to service any of the subscriberterminals supported by the gateway, even if the Field of Regard ofsatellite 2 does not illuminate the gateway because the gateway isbehind the Field of Regard, as depicted in FIG. 49D (step 1450). In step1452, the gateway will break the connection with satellite 2 ifsatellite 2 has moved to an orbital position which it can no longerservice any terminal supported by the gateway. For example, FIG. 49Eshows a Field of Regard of satellite 2 east of coverage areas B1, B2,B3, B4 and B5.

Synchronization

Because of the timing as discussed above, it is important that thesatellites, subscriber terminals and gateways all remain in tightsynchronization. In one embodiment, a master clock is maintained andaccessed at a terrestrial location. For example, the master clock can bemaintained by or at the network control center. As each satellite passesover or near the network control center, the satellites will synchronizewith the network control center, or synchronize with the master clock.The gateways will then synchronize with each satellite prior toconnection with the satellite so that the gateways are now insynchronization with the satellite they are communicating with. Thesubscriber terminals will be responsible for maintaining synchronizationwith the gateways. In this system, each satellite comprises an antennasystem that is configured to receive command information from a groundcenter (e.g., network control center) includes a command to adjust aclock on the satellite to synchronize the satellite to a master clock.The satellite also sends a beacon signal toward the Earth (i.e., towardmultiple gateways). The beacon signal includes timing information tosynchronize the gateway to the satellite. The gateways are configured tocommunicate with the satellite and with the terminals via the satellite.The gateway is configured to receive the beacon signal from thesatellite and synchronize to the satellite based on the beacon signal.The gateway is configured to send communication to the terminal via thesatellite. The communication includes timing data for the terminalsynchronize to the gateway.

FIG. 50 is a flow chart describing one embodiment of a process forperforming timing synchronization for the satellite communicationsystem. In step 1502, network control system 230 (FIG. 1) maintains amaster clock. In step 1504, as the satellite passes above or near thenetwork control center (or to the nearest location to the networkcontrol center in its orbit), the network control center sends a timingmessage that includes a command to set the clock on the satellite. Thenetwork control center may also send one or more hopping plans. In oneembodiment, the master clock is maintained at the network controlcenter. In another embodiment, the master clock is maintained at anotherlocation but the network control center can access the master clock andsend the command to the satellite. That command can set the satellite'sclock to the master clock or to adjust the satellite's clockaccordingly. In step 1506, in response to receiving the command, thesatellite clock sets or otherwise updates its clock to the master clock,thereby synchronizing the satellite to the master clock (andsynchronizing the satellite to the network control center).

In step 1508, the satellite transmits a beacon signal that includestiming information. The beacon signal is a broad beam that may cover theentire face of the planet that can be seen by the satellite. In step1510, prior to establishing communication with the satellite (prior toestablishing communication with subscriber terminals via the satellite)for the current orbit, the gateway synchronizes with a satellite usingthe satellite's beacon signal (timing synchronization aligns the gatewayforward burst with the allocated time slot reference on the satellitewhile accounting for delay and Doppler—see step 1432 of FIG. 48). Thegateway will then establish communication with the satellite toimplement connections between the gateway and a plurality of subscriberterminals via the satellite. In step 1512, the gateway sendscommunication to the subscriber terminals via the satellite, thatcommunication includes timing data. In step 1514, subscriber terminalssynchronize to the gateway during the communication based on the timingdata, aligning the subscriber terminal timing with the satellite clock.In one embodiment, the communication includes user data so that thesubscriber terminal synchronizes to the gateway while communicating userdata with the gateway.

FIG. 51 is a flow chart describing more details of the process forsynchronizing the gateway. In one embodiment, the process of FIG. 51 isone example implementation of step 1510 of FIG. 50. In step 1532, thesatellite transmits and the gateway receives the high frequency beaconsignal that was broadcast to the entire visible surface of the planet.The beacon signal indicates start of an epoch and a number of epochssince midnight. In one embodiment, the entire satellite communicationsystem has an agreed upon midnight. Note that midnight occurs atdifferent times on the planet (i.e., difference time zones) so, in oneembodiment, the system picks a single time reference to be the officialmidnight of the satellite system. In step 1534, using satelliteephemeris data (satellite orbit and previous time tagged locations) thegateway determines where the satellite currently is. In step 1536, basedon the determined location, the gateway calculates the current time ofday for the gateway (relative to epoch and epoch counts in systemmidnight). In step 1540, the gateway uses the timing beacon to furtheradjust its clock based on the calculated current time of day. In step1542, the gateway receives one or more new hopping plans via theinternet (or other network) from the network control center in order toimplement in the future.

FIG. 51A provides one example of a beacon signal. In one exampleembodiment, the beacon signal includes a set of pulses, where the periodof pulses is equal to one epoch as depicted in FIG. 51A. The beaconsignal will also include a Message Block that indicates the distance intime from system midnight. The Message Block ends each set of a periodof time that the gateway knows which epoch within the time of day windowthe epoch corresponds with. In this case, one hundred epochs (Century).Thus, the first pulse after a Message Block is the start of a newCentury. Each message block will identify which century it is in.Therefore, the gateway upon receiving a message block can determine howmany epochs there have been since midnight. Additionally, the gatewaycan use the timing of the pulses to determine when an epoch starts andtherefore adjust its clock accordingly.

In one embodiment, the gateway does not tell the subscriber terminalswhat epoch it may communicate in. This process is described in moredetail by the flow chart of FIG. 52, which is one example ofimplementation of step 1514 of FIG. 50. In step 1560, the subscriberterminal is always looking for the header of a super-frame in the downlink. The header contains a unique sequence of bits. Therefore, in oneembodiment, the subscriber terminal does not need to know the hoppingplan because the subscriber terminal is always looking for the uniquesequence of bits. When the subscriber terminal's beam is not active, thesubscriber terminal will not see that unique sequence of bits. In step1562, the subscriber terminal detects the header of the super-frame inthe down link. In step 1564, the subscriber terminal uses the symbolphases in the header to adjust its clocking/timing so that thesubscriber terminal is now in synchronization with the gateway. In somecases, the gateway will include clock information, date information orother timing information in the payload of the super-frame. If the timeof day is in the super-frame, then the subscriber terminal willcalculate the current time of day from the subscriber terminal based onthe time of day in the super-frame and transmission delay. In step 1570,the calculated current time is used to adjust the clock for thesubscriber terminal. If the time of day is not in the super-frame, thenno further adjustment is made to the timing (step 1572).

In one embodiment, the gateway will instruct the subscriber terminalwhen to transmit on the up link and what frequency to use. This willenable the subscriber terminal to transmit when its hopping beam isactive, without having to know the full hopping plan.

In one embodiment, when a subscriber terminal is connected to multiplegateways, the subscriber terminal establishes independent timing even ifthe gateways are communicating over the same satellite. Thus, s firstgateway and a second gateway connected to the same subscriber terminalvia the same satellite are configured to establish independent (ieseparate) timing with the subscriber terminal.

Note that in the above discussion of FIG. 51, the gateway used ephemerisdata to calculate the satellite's current location. FIG. 53 is a flowchart describing one embodiment describing one embodiment for aplurality of gateways to determine ephemeris data for a satellite. Theprocess of FIG. 53 can be performed for each satellite multiple timesday. In step 1580, multiple gateways receive a GPS signal from themultiple GPS satellites. In step 1582, these gateways will identify GPStime based on those received GPS signals using known methods. In step1584, the multiple gateways will receive the beacon signal from aparticular satellite. Each of the gateways will determine the time ofreceipt of that beacon signal in GPS time. All the gateways transmit(via the internet or other network) their receive times (in GPS time) ofthat beacon signal to other gateways. Each of the gateways calculate thelocation and velocity of the satellite based on the beacon signalreceived times at each gateway and the known locations of each gateway.This assumes that the gateways are not mobile. This process can alsomake use for multiple samples of the beacon signal. By knowing thelocation of a gateway and the time it took to transmit a beacon signalfrom the satellite to the gateway, it can be calculated how far thesatellite is from the gateway. That creates a sphere around the gatewaywhere the satellite can be anywhere on the surface of that sphere. Butknowing that sphere from multiple gateways, there will be anintersection point that intersects all the spheres, which represents thelocation of the satellite at the moment and time. By calculating thesatellite at multiple times, the satellite location and velocity can becalculated. By knowing the proposed orbit and a bunch of samples oflocation and velocity, the gateway can predict the location of thesatellite at any given time. If the process of FIG. 53 is performedmultiple times a day, then the gateway's ephemeris data will remaincurrent.

One embodiment also includes determining the Doppler to the satelliteincluding receiving the beacon signal at the ground based gateway,determining frequency offset over time of the beacon signal at theground based gateway; and calculating Doppler to the satellite using thehistory of the beacon signal frequency offset.

As described above, in one embodiment, the non-geostationary satellitesare configured to provide steerable gateway beams and non-articulatedgateway beams. The non-geostationary satellite includes a beam hoppingplan for the plurality of spot beams using time domain beam hopping, abeam steering plan for the steerable gateway beams, a steering plan forthe high capacity beams and a connectivity plan for on-board routingbetween the gateway beams and the plurality of spot beams using timedomain beam hopping, The hopping plan and the connectivity plan arestructured as a sequence of epochs.

In some embodiments the satellite clock is adjusted during thereconfiguration time, and/or the clock on the satellite is adjusted by aterrestrial location (e.g., network control center 230, a gateway orother terrestrial location) in burst of small increments periodicallywhile the satellite is in view.

Note that the discussion above introduces many different features andmany embodiments. It is to be understood that the above-describedembodiments are not all mutually exclusive. That is, the featuresdescribed above (even when described separately) can be combined in oneor multiple embodiments.

One embodiment includes a method of operating a satellite communicationssystem, comprising: accessing master clock information at a terrestriallocation; transmitting a timing message based on the master clockinformation from the terrestrial location to a satellite as thesatellite is in orbit; synchronizing the satellite to the master clockbased on the timing message; transmitting a beacon signal from thesatellite, the beacon signal includes timing information; receiving thebeacon signal at a ground based gateway; synchronizing the gateway tothe satellite based on the beacon signal; sending communication from thegateway to a terminal via the satellite, the communication includestiming data; and synchronizing the terminal to the gateway based on thetiming data.

One embodiment includes a satellite communication system, comprising: asatellite comprising an antenna system configured to receive commandinformation from a ground location and transmit a beacon signal toward aground based gateway, the command information includes a command toadjust a clock on the satellite to synchronize the satellite to a masterclock, the beacon signal includes timing information to synchronize thegateway to the satellite.

One embodiment includes a satellite based communication system,comprising: a gateway configured to communicate with a terminal via thesatellite, the gateway is configured to receive a beacon signal from thesatellite and synchronize to the satellite based on the beacon signal,the gateway configured to send communication to the terminal via thesatellite, the communication with the terminal includes timing data forthe terminal to synchronize to the gateway.

For purposes of this document, it should be noted that the dimensions ofthe various features depicted in the figures may not necessarily bedrawn to scale.

For purposes of this document, reference in the specification to “anembodiment,” “one embodiment,” “some embodiments,” or “anotherembodiment” may be used to describe different embodiments or the sameembodiment.

For purposes of this document, a connection may be a direct connectionor an indirect connection (e.g., via one or more others parts). In somecases, when an element is referred to as being connected or coupled toanother element, the element may be directly connected to the otherelement or indirectly connected to the other element via interveningelements. When an element is referred to as being directly connected toanother element, then there are no intervening elements between theelement and the other element. Two devices are “in communication” ifthey are directly or indirectly connected so that they can communicateelectronic signals between them.

For purposes of this document, the term “based on” may be read as “basedat least in part on.”

For purposes of this document, without additional context, use ofnumerical terms such as a “first” object, a “second” object, and a“third” object may not imply an ordering of objects, but may instead beused for identification purposes to identify different objects.

For purposes of this document, the term “set” of objects may refer to a“set” of one or more of the objects.

The foregoing detailed description has been presented for purposes ofillustration and description. It is not intended to be exhaustive or tolimit the subject matter claimed herein to the precise form(s)disclosed. Many modifications and variations are possible in light ofthe above teachings. The described embodiments were chosen in order tobest explain the principles of the disclosed technology and itspractical application to thereby enable others skilled in the art tobest utilize the technology in various embodiments and with variousmodifications as are suited to the particular use contemplated. It isintended that the scope of be defined by the claims appended hereto.

What is claimed is:
 1. A method of operating a satellite communicationssystem, comprising: accessing master clock information at a terrestriallocation; transmitting a timing message based on the master clockinformation from the terrestrial location to a satellite as thesatellite is in orbit; synchronizing the satellite to the master clockbased on the timing message; transmitting a beacon signal from thesatellite, the beacon signal includes timing information; receiving thebeacon signal at a ground based gateway; synchronizing the gateway tothe satellite based on the beacon signal; sending communication from thegateway to a terminal via the satellite, the communication includestiming data; and synchronizing the terminal to the gateway based on thetiming data.
 2. The method of claim 1, wherein: the timing messageincludes a command to set a clock on the satellite.
 3. The method ofclaim 1, wherein: the beacon signal indicates timing of an epoch fortime domain beam hopping and indicates a quantity of epochs from a timereference.
 4. The method of claim 1, wherein: the satellite receives thetiming message as the satellites travels in orbit closest to theterrestrial location.
 5. The method of claim 1, wherein: the satelliteis a non-geostationary satellite.
 6. The method of claim 1, wherein: theterminal synchronizes to the gateway while communicating user data withthe gateway.
 7. The method of claim 1, further comprising: establishingcommunication between the gateway and the satellite to implementconnections between the gateway and a plurality of terminals via thesatellite, the synchronizing the gateway to the satellite based on thebeacon signal is performed before the establishing communication for acurrent orbit.
 8. The method of claim 1, wherein: the sendingcommunication from the gateway to the terminal includes sending a frame,the timing data is in the frame.
 9. The method of claim 1, wherein: thesynchronizing the gateway to the satellite based on the beacon signalcomprises using a location of the satellite and a location of thegateway to determine a transmission delay of the beacon signal andadjusting timing on the gateway based on the timing information in thebeacon signal and the transmission delay.
 10. The method of claim 9,further comprising: determining the location of the satellite including:receiving GPS signals at a ground based gateway; receiving the beaconsignal at the ground based gateway; determining time of receipt in GPStime of the beacon signal at the ground based gateway; and calculatinglocation of the satellite using the time of receipt in GPS time of thebeacon signal at the multiple ground based gateways.
 11. The method ofclaim 9, further comprising determining the Doppler to the satelliteincluding receiving the beacon signal at the ground based gateway,determining frequency offset over time of the beacon signal at theground based gateway; and calculating Doppler to the satellite using thehistory of the beacon signal frequency offset.
 12. The method of claim9, further comprising determining the location of the satelliteincluding: receiving GPS signals at multiple ground based gateways;identifying GPS time at the multiple gateways; receiving the beaconsignal at the multiple ground based gateways; determining times ofreceipt in GPS time of the beacon signal at the multiple ground basedgateways; and calculating location of the satellite using the times ofreceipt in GPS time of the beacon signal at the multiple ground basedgateways.
 13. A satellite communication system, comprising: a satellitecomprising an antenna system configured to receive command informationfrom a ground location and transmit a beacon signal toward a groundbased gateway, the command information includes a command to adjust aclock on the satellite to synchronize the satellite to a master clock,the beacon signal includes timing information to synchronize the gatewayto the satellite.
 14. The satellite communication system of claim 13,wherein: the satellite clock is adjusted during the reconfigurationtime; and the beacon signal indicates timing of an epoch for time domainbeam hopping and indicates a quantity of epochs from a time reference.15. The satellite communication system of claim 13, wherein: thesatellite is a non-geostationary satellite.
 16. The satellitecommunication system of claim 13, wherein: the satellite is anon-geostationary satellite; and the clock on the satellite is adjustedby the terrestrial location in burst of small increments periodicallywhile the satellite is in view.
 17. The satellite communication systemof claim 13, further comprising: the gateway, synchronizing the gatewayto the satellite includes using a location of the satellite and alocation of the gateway to determine a transmission delay of the beaconsignal and adjusting timing on the gateway based on the timinginformation in the beacon signal and the transmission delay.
 18. Thesatellite communication system of claim 17, wherein: the gateway isconfigured to determine the location of the satellite by working withother gateways to receive GPS signals at multiple ground based gateways,identify GPS time at the multiple gateways, receive the beacon signal atthe multiple ground based gateways, determine times of receipt in GPStime of the beacon signal at the multiple ground based gateways andcalculate location of the satellite using the times of receipt in GPStime of the beacon signal at the multiple ground based gateways.
 19. Asatellite based communication system, comprising: a gateway configuredto communicate with a terminal via the satellite, the gateway isconfigured to receive a beacon signal from the satellite and synchronizeto the satellite based on the beacon signal, the gateway configured tosend communication to the terminal via the satellite, the communicationwith the terminal includes timing data for the terminal to synchronizeto the gateway.
 20. The satellite communication system of claim 19,wherein: the beacon signal indicates timing of an epoch for time domainbeam hopping and indicates a quantity of epochs from a time reference.21. The satellite communication system of claim 19, wherein: the gatewayis configured to establish communication between the gateway and thesatellite to implement connections between the gateway and a pluralityof terminals via the satellite, the gateway configured to synchronize tothe satellite based on the beacon signal before the establishingcommunication for a current orbit.
 22. The satellite communicationsystem of claim 19, wherein: the gateway is configured to synchronize tothe satellite based on the beacon signal by using a location of thesatellite and a location of the gateway to determine a transmissiondelay of the beacon signal and adjusting timing on the gateway based onthe timing information in the beacon signal and the transmission delay.23. The satellite communication system of claim 22, wherein: the gatewayis configured to determine the location of the satellite by working withother gateways to receive GPS signals at multiple ground based gateways,identify GPS time at the multiple gateways, receive the beacon signal atthe multiple ground based gateways, determine times of receipt in GPStime of the beacon signal at the multiple ground based gateways andcalculate location of the satellite using the times of receipt in GPStime of the beacon signal at the multiple ground based gateways.
 24. Thesatellite communication system of claim 19, wherein: an additionalgateway, the gateway and the additional gateway are connected to theterminal via the satellite, the gateway and the additional gateway areconfigured to establish independent timing with the terminal.